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
Answer:
rental charge per day = 17 $
rental charge per mile = 1/10 $