ANSWER
$3
Or
$4
EXPLANATION
The revenue function is

The cost function is,
C=600-50t
In order to break even, revenue must be equal to cost.

Group every term on the LHS.


Divide through by 50.

Factor to obtain,


It would come out to be $41.8275, so if you round it would cost $41.83.
70/x=100/120
(70/x)*x=(100/120)*x - we multiply both sides of the equation by x
70=0.833333333333*x - we divide both sides of the equation by (0.833333333333) to get x
70/0.833333333333=x
84=x
x=84
now we have:
<span>120% of 70=84</span>