Hints on some homework questions:

 Section 1.4 # 71: 

(a). Use 

(b). Set the equation above equal to 500 and solve for t.

Section 1.6 # 58

Total cost of car A after t years  is : 10,000 + 550t + 625t=10000 + 1175t

Total cost of car B after t years  is: 12,000 + 600t + 375t=12000 + 975t.