Step-by-step Answer:
It is a problem involving the setting up of two linear equations to form a system of two equations, and subsequently solving the system for equality.
Let M=number of miles/day
Agency A:
Ca=cost at agency A for 1 day = 19+0.10M
Agency B:
Cb=cost at agency B for 1 day = 26+0.07M
When the cost of rental for 1 day are equal, Ca=Cb, or
19+0.10M = 26+0.07M
Transpose
0.10M-0.07M = 26-19 = 7
0.03M = 7
M=7/0.03=233.333
The theoretical number of miles ( per day) for the rental costs to be equal is 233.3 miles.
However, since it appears that fractional miles are counted as one mile, we could say
233 miles (per day) or below, agency A is more economical
234 miles (per day) or above, agency B is a better bet.
Big thank to wegnerkolmp2741o for spotting the mistake, which allowed me to make the correction required.