Question 1073884
xy = 280
x = 4y-12
(4y-12)y = 280
4y^2-12y-280 = 0
y^2-3y-70 = 
(y+7)(y-10)
y = -7 or y = 10
Let's try the 10 first:
(4(10)-12)10 = 280
28*10 = 280 Correct, y = 10
x = 4y-12 = 40-12 = 28
:
John