Best rentals charges a daily fee plus a mileage fee for renting its cars. barney was charged $81 for 3 days and 300 miles, while mary was charged $145 for 5 days and 600 miles. what does best rental charge per day and per mile?

For this case, the first thing we must do is define variables:
 x: rental charge per day
 y: rental charge per mile
 We write the system of equations:
 3x + 300y = 81
 5x + 600y = 145
 Solving the system we have:
 x = 17
 y = 1/10
 
 rental charge per day = 17 $
 rental charge per mile = 1/10 $