Question

A rental car agency charges a flat fee of $139.00 plus $30.00 per day to rent a certain car. Another agency charges a fee of $13.00 plus $51.00 per day to rent the same car. Find the number of days for which the costs are the same. Round your answer to the nearest whole day.

Answer 1

139 + 30d = 13 + 51d
139 - 13 = 51d - 30d
126 = 21d
126/21 = d
6 = d

now lets check..
139 + 30d = 139 + 30(6) = 319
13 + 51d = 13 + 51(6) = 319

so on day 6, they will both cost $ 319