Answer:
at
![x=4](https://img.qammunity.org/2020/formulas/mathematics/high-school/hxnxycp7ditjozikbfiiya3nb2g21vrzay.png)
Explanation:
Given: The length of the rectangle is
and width of the rectangle is
![3x+1](https://img.qammunity.org/2020/formulas/mathematics/middle-school/8zr6bm5to26088m0zqkuxprfyd8s5rws0b.png)
To find: An expression that can be used to find the perimeter of the rectangle, and the perimeter when x is 4.
Solution:
Here, Length is given as
width of the rectangle is
![3x+1](https://img.qammunity.org/2020/formulas/mathematics/middle-school/8zr6bm5to26088m0zqkuxprfyd8s5rws0b.png)
Let P represents the perimeter of the rectangle
We know that perimeter of a rectangle is
![2(l+w)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/p49vgs78g7ez85c1uxd9mdp575mu2q8f8e.png)
So, we have
![P=2(l+w)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/iuzrgc5ydahb9ojuqi0cm1ha7m7zobnpkl.png)
![P=2(5x-2+3x+1)](https://img.qammunity.org/2020/formulas/mathematics/high-school/zask68glf9f97ri7pv6zwohpnjlspu2yue.png)
![P=2(8x-1)](https://img.qammunity.org/2020/formulas/mathematics/high-school/zxzfcwocvrku81ycryqy87w6kuj8y0nma2.png)
Therefore, the expression to find the perimeter is
![P=2(8x-1)](https://img.qammunity.org/2020/formulas/mathematics/high-school/zxzfcwocvrku81ycryqy87w6kuj8y0nma2.png)
Now, we need to find the perimeter at
On substituting
in
we have,
![P=2(8(4)-1)](https://img.qammunity.org/2020/formulas/mathematics/high-school/uc3keunz98v4mq6390aefnekdsskmw8hoe.png)
![P=2(32-1)](https://img.qammunity.org/2020/formulas/mathematics/high-school/autt2x1ja5q09g0gqh0h8e3orubu7616ak.png)
![P=2(31)](https://img.qammunity.org/2020/formulas/mathematics/high-school/hxytp2bbm7ekpp2sz8rf7qynimspg7iemg.png)
![P=62](https://img.qammunity.org/2020/formulas/mathematics/high-school/f90bnj5xm9jx4jb843rllt1jiph382n6sh.png)
Hence, the perimeter is 62 units when x is 4.