The cost of renting a moving van for a 26 mile trip is $62.50. the cost of renting the same van for a 38 mile trip is $65.50 the cost changes at a constant rate with the respect to length (in miles) of the trip. find the total cost of renting the van for a 54 mile trip.

The difference between the 26 mile trip and 38 mile trip is 12 miles.
The difference in the price is $3.00   ($65.50 - $62.50)

So those 12 miles cost $3.00     $3.00÷12 = $.25 per mile

We can use either given trip to solve.  I will use the 38  mile trip.
The difference between 38 miles and 54 miles is 16 miles.   At $.25 a mile those 16 miles will add $4.00 to the price.  ($.25 x 16 = $4.00)
Since the 38 mile trip costs $65.50 we add $4.00 and get $69.50 for a 54 mile trip.