SOLUTION
(a) The first plan cost $55 and an additional $0.13 per mile driven,
while the second plan cost $48 and an additional $0.17 per mile driven
Let the amount of driving be x
Then, this means that for the first plan we have

And the second plan becomes

So, for the plans to cost the same for a particular amount of driving x, it means that

Collecting like terms we have

Hence the two plans cost the same at 175 miles
(b) The cost when the two plans cost the same is

Hence the answer is $77.75