Your "y =35+0.25" would be better if written as y =$35/wk + ($0.25/mile)x, where x is the # of miles traveled and we assume that you rent the car for 1 week or less.
Now let's evaluate y =$35/wk + ($0.25/mile)x for x = 60 mi:
First thing you have to do is take the 5 + -8 which equals -3 then you have to 33-18 which equals 15 then u have to divide by the -3 which gives you equal your answer of -5
