A railroad crew can lay 5 miles of track each day. They need to lay 140 miles of track. The length, L (in miles), that is left to lay after d days is given by the following function.
L(d) = 140-50
Answer the following

(a) How many days will it take the crew to lay all the track?
I days

(b) How many miles of track does the crew have left to lay after 18 days?
miles