Hi there! Hopefully this helps!
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Answer: p = 21
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![p - 18 = 3](https://img.qammunity.org/2021/formulas/mathematics/college/zq7v5u87alnc3t2wo05wzwbemkau0r87et.png)
Add 18 to both sides.
![p = 3 + 18](https://img.qammunity.org/2021/formulas/mathematics/college/l3nhle8okvqyfr490j4cdf2lvwqxbm8icl.png)
Add 3 and 18 to get, you guessed it, 21!