A railroad crew can lay 7 miles of track each day. They need to lay 196 miles of track. The length, L (in miles), that is left to lay after d days is given by the following function.
L (d) = 196 - 7d
(a). How many days will it take the crew to lay all the track?
(b) How many miles of track does the crew have left to lay after 19 days?