Write equations for both then find the point of intersection.
Company A:
$40 a day
y = 40x
Company B:
$60 fee, $20 a day
y = 20x + 60
We can plug in '40x' for 'y' in the 2nd equation:
y = 20x + 60
40x = 20x + 60
Subtract 20x to both sides:
20x = 60
Divide 20 to both sides:
x = 3
So in 3 days the cost will be the same.