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6x(280)-280(6(x-20)=7x(x-20)
7x^2 - 560x + 5600
nope! the robot tutor is wrong again
6x(280)-280(6(x-20)=7x(x-20)
divide each term by 7
6x(40) - 40(6x - 120) = x^2 - 20x
240x - 240x + 4800 = x^2 - 20x
x^2 - 20x - 4800 = 0
(x - 80)(x + 60) = 0
x = 80 or x = -60