The question is not perfectly clear, but I assume you're asking something like this:
in a rectangle, the area is given by
![A=wl](https://img.qammunity.org/2020/formulas/mathematics/middle-school/2g3br4owbx6si7e4ymnqogbpukuhkyxkvi.png)
where A is the area, w is the width and l is the length.
So, if we know that the width is 7 and we let x be the length of the rectangle, we have
![A=7x](https://img.qammunity.org/2020/formulas/mathematics/middle-school/7gbmehm2hkz4xt8a3cn4l5zowyt4373orh.png)
If you need to solve this for x, divide both sides by 7:
![x=(A)/(7)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/5pckw2n1g5j6gg7zilfot54q5hh1k11k5a.png)