Twice the square of a certain whole number added to 3 times the number makes 90 find the number

2(x^2) + 3x = 90

2(x^2) + 3x - 90 = 0
find 2 factors of 2 and -90 that add to 3
2*-90 = -180 = 15*-12
2(x^2) - 12x + 15x - 90 = 0
2x(x-6) + 15(x-6) = 0
(2x+15)(x-6) = 0
2x + 15 = 0
2x = -15
x = -7.5 <-- not a whole number; cannot be answer
x-6 = 0
x = 6 <-- is a whole number; this is the answer