We can interpret the costs for each taxi into these equations:

Let x = cost of renting Taxi X per day driving m miles, y = cost of renting Taxi X per day driving m miles.
$x = 10 + 0.25m$
$y = 20 + 0.10m$

Given that $y(m) < 25$, we can set up this inequality:
$20 + 0.10m < 25 m < 50$

Plug m = 50 back into Taxi X's equation:
$x(50) = 10 + 0.25(50) = 22.5$

However since we know that m is LESS than 50, the total amount will be LESS than 22.5.
You could double check by using any value of m less than 50, e.g., 40:
$x(40) = 10 + 0.25(40) = 20 < 22.5$