Question 705264
For 1st 1/2 hr, student pays $3 and has $4 left
Add  1 hr, now = 1.5 hrs, student pays $1.50,
has $4 - $1.50 = $2.50 left
Add 1 hr, now = 2.5 hrs
has $2.50 - $1.50 = $1 left
Anything over the 2.5 hrs, the student will be 
charged $1.50, but only has $1, so
2.5 hrs is the maximum time with $7