Question 1003123
The description needs to be stated better, but it is still understandable.

{{{x^2}}} is the area of the picture.
{{{(x+2*8)(x+2*6)}}} is the total area of frame plus picture.
Total area, which is also the "total area of frame plus picture", is 320 square cm.


Put the last two parts of the analysis together:
{{{highlight_green((x+16)(x+12)=320)}}}

You should have no real trouble solving the quadratic equation.  Just several arithmetic and a few simplification steps.