You can estimate the answer (correctly) by observing that 3 × 70 is 210. This is close enough to 232.85 that you know the number of rental days is not 2 or 4.
The equation for the number of days (d) is ...
73.95d +11 = 232.85 . . . $73.95 per day plus an extra fee
73.95d = 221.85 . . . . . . subtract 11
d = 221.85/73.95 = 3 . . . . divide by the coefficient of d
