Answer:
P(n)=5n+9
Step-by-step explanation:
The initial population (week 0), 
Population after 5 weeks, 
Since the population is growing according to a linear growth model.
A linear model is of the form: y=mx+b where m is the slope and b is the y-intercept.
First, we determine the population growth per week which is our slope.

We then have:
y=5n+b
When Number of weeks, n=0,
=y=9
Therefore: 9=5(0)+b
b=9
Therefore, our population after n weeks:
P(n)=5n+9