Question 450034
Let d = the daily fee
Let m = the mileage charge
For Barney's charges we can write:
69 = 3d + 300m [3 day rental, 300 mi]
For Mary's charges, we can write:
123 = 5d + 600m [ 5 day rental, 600 mi]
We have two equations and two unknowns so we can solve.
Multiplying the 1st equation by 2 and subtracting the 2nd gives:
138 - 123 = 6d - 5d
15 = d
Now we can use this value for d to solve for m.  From the 1st equation above, we have:
69 = 3(15) + 300m
24/300 = m = 0.08
Therefore, the daily fee is $15 and the mileage charge is $0.08 per mile.