Question 3170
The previous work is good:

36 = 1/2(4x + 2)*(x)

which evaluates to our quadratic 

2x^2  + x -36 = 0

This does factor nicely

(2x + 9)(x - 4)

We take the positive 0; so x = 4.

36 = 1/2( (4 * 4 )+ 2) (4)
As we can see, this does check.