So we can see that the two angles form a "c." This c indicates that it is a same side interior angle. Same side interioir angles are equal to 180 degrees. So, set both the expressions to 180.
Your surface area is: S=x^2+4xh=84 square inches and h=2 inches; so you get: x^2+(4×2)x=84 x^2+8x-84=0 qhich is a quadratic equation. Using the quadratic formula you get two results for x: x1=-14 and x2=6 choose the second (positive)
