The number of cars sold weekly by a new automobile dealership grows according to a linear growth model. The first week the dealership sold seven cars ($\displaystyle {P}_{{0}}={7}$). The second week the dealership sold eight cars ($\displaystyle {P}_{{1}}={8}$).

The recursive formula for the number of cars sold, $\displaystyle {P}_{{N}}$, in the ($\displaystyle {N}+{1}$)^th week has form:

Where:
a =

The explicit formula for the number of cars sold, $\displaystyle {P}_{{N}}$, in the ($\displaystyle {N}+{1}$)^th week has form

Where
b =
c =

If this trend continues, how many cars will be sold in the fourth week?

cars

In each box, enter a single number. Do not leave any boxes blank (enter 1 or 0 as appropriate if necessary).