Hello,
I think it is 9y² + 21y - 18 = 0
we have a = 9 ; b = 21 and c = -18
∆ = b² - 4ac = 21² - 4 × 9 × (-18) = 1089 > 0
x1 = (-b - √∆)/2a = (-21 - 33)/9 = 6
x2 = (-b + √∆)/2a = (-21 + 33)/9 = 12/9 = 4/3
S = {4/3 ; 6}
