Question 380097
The area is just (x)(x - 3.5) = 15 -->

{{{x^2 - 3.5x - 15 = 0}}}

{{{2x^2 - 7x - 30 = 0}}}

{{{(2x + 5)(x - 6) = 0}}}

x = -5/2 or x = 6. We take the positive value x = 6 and check: 6(6 - 3.5) = 15.