He will earn $480 after 2 years
U subtract 4x by 5x and then you add 3 by -21 and the answer is x=18
First, subtract k from both sides. That means c - k is in the left side and 3x is on the right. Then, divide by 3 on both sides. So, the answer is x = (c - k) / 3.
Just to confirm is it x-5/8 or (x-5)/8
lets assume one number is x
then 2nd number will be 5x-2
so product is 120
x (5x-2) = 120
5x^2 - 2x = 120
so answer is last option