Let's make two expressions.
4.92+3.79x
This represents the car service's cost, which x being miles.
4.2x
This is the most Jason wants to spend. Let's make them equal.
4.92+3.79x=4.2x
We need to get x by itself, Let subtract 3.79x from both sides.
4.92=0.41x
Let's divide.
4.92÷0.41=12
So, he should not drive no more than 12 miles.