Answer:
![9 (9)/(11)](https://img.qammunity.org/2023/formulas/mathematics/high-school/v73xlyzr0fzo10busgg9myooptj6yzzyut.png)
Explanation:
Let the unknown number be x.
Given equation:
![3 (1)/(4) + (2)/(3)x=12 (1)/(4)-(1)/(4)x](https://img.qammunity.org/2023/formulas/mathematics/high-school/io3xt1nx8rsg9rdxaabkwkie8453i6tz7f.png)
![\textsf{Add\; $(1)/(4)x$ \;to\;both\;sides\;of\;the\;equation}:](https://img.qammunity.org/2023/formulas/mathematics/high-school/9vks83s1xpf8g3co0grtqdflh331ynqvk2.png)
![\implies 3 (1)/(4) + (2)/(3)x+(1)/(4)x=12 (1)/(4)-(1)/(4)x+(1)/(4)x](https://img.qammunity.org/2023/formulas/mathematics/high-school/xbxw54u05s8zby8ubf4qfxl42oymazm7yt.png)
![\implies 3 (1)/(4) + (2)/(3)x+(1)/(4)x=12 (1)/(4)](https://img.qammunity.org/2023/formulas/mathematics/high-school/syoiokaper01aozef1a9ucht3oe1htriy6.png)
![\textsf{Subtract\; $3(1)/(4)$ \;from\;both\;sides\;of\;the\;equation}:](https://img.qammunity.org/2023/formulas/mathematics/high-school/tgi6mnbapxxf8qlz7ce97n6f5fh1rqjsvx.png)
![\implies 3 (1)/(4) + (2)/(3)x+(1)/(4)x-3 (1)/(4)=12 (1)/(4)-3 (1)/(4)](https://img.qammunity.org/2023/formulas/mathematics/high-school/7rftufp3vaqely4xb0kunfw1bjhouh3qg7.png)
![\implies (2)/(3)x+(1)/(4)x=12 (1)/(4)-3 (1)/(4)](https://img.qammunity.org/2023/formulas/mathematics/high-school/txhvn494jigh3df4tpk2oryqrp8dpdsek8.png)
Subtract the mixed numbers:
![\implies (2)/(3)x+(1)/(4)x=9](https://img.qammunity.org/2023/formulas/mathematics/high-school/80ixe9p2bm3sgjtwhktzqok42wx5ik5fq3.png)
When adding fractions with different denominators, multiply the numerator and the denominator of each fraction by the same amount to make the denominators the same:
![\implies (4)/(4) \cdot (2)/(3)x+(3)/(3) \cdot (1)/(4)x=9](https://img.qammunity.org/2023/formulas/mathematics/high-school/kp5vl5drz7uj6qj089by46txw4uxpu8nqw.png)
![\implies (8)/(12)x+(3)/(12)x=9](https://img.qammunity.org/2023/formulas/mathematics/high-school/gpqsyqo8153xj54boyq06no3sv58fc88u5.png)
Add the fractions:
![\implies \left((8)/(12)+(3)/(12)\right)x=9](https://img.qammunity.org/2023/formulas/mathematics/high-school/w7doya4lkuq88c6k3qorbm6y2vqaplz51d.png)
![\implies (11)/(12)x=9](https://img.qammunity.org/2023/formulas/mathematics/high-school/38mq30c82bsodewy59u7muol4jfaxc9ima.png)
Multiply both sides by 12:
![\implies 12 \cdot (11)/(12)x=12 \cdot 9](https://img.qammunity.org/2023/formulas/mathematics/high-school/dgtmsey9hwbn9bai6toe4q12zs35xqj0w0.png)
![\implies 11x=108](https://img.qammunity.org/2023/formulas/mathematics/high-school/wcy9jlcx08a93e8fmjx5jogw5dm8kwtmw9.png)
Divide both sides by 11:
![\implies (11x)/(11)=(108)/(11)](https://img.qammunity.org/2023/formulas/mathematics/high-school/o3dxyvulh4f5tonek5e5el6p45fcpv46hr.png)
![\implies x=(108)/(11)](https://img.qammunity.org/2023/formulas/mathematics/high-school/poc82xecf8syo87mu2r9haamz462l8ioc6.png)
To convert the fraction into a mixed number, divide the numerator by the denominator:
![\implies 108 / 11 = 9\; \textsf{remainder}\;9](https://img.qammunity.org/2023/formulas/mathematics/high-school/xk4zug6nxhjci1nxzctzey45kydlormkpx.png)
The mixed number answer is the whole number and the remainder divided by the denominator:
![\implies x=9 (9)/(11)](https://img.qammunity.org/2023/formulas/mathematics/high-school/m9vvtuw8uc46a7zs8bscspf89oldh1xhlq.png)