Martina spends $15 each time she travels the toll roads. She started the month with $225 in her toll road account. The amount, A (in dollars), that she has left in the account after trips on the toll roads is given by the following function. A(t)=225-15t

Answer the following questions.

a. How many trips on the toll roads can Martina take until her account is empty?

b. How much money does she have left in the account after 8 trips on the toll roads?