Step-by-step explanation:
x² - 9x = 36
x² - 9x - 36 = 0
x² + 3x - 12x - 36 = 0
x ( x + 3 ) - 12 ( x + 3 )
( x - 12 ) ( x + 3 )
x = 12, -3
sum = 12 + (-3)
= 12 - 3
= 9
