Constructing Linear and Exponential Functions Practice Test

If $f$ is linear, $f(0)=8$, and $f(4)=20$, what is $f(x)$? Write in the form $f(x)=mx+b$.

A bacteria culture starts with 200 bacteria and grows by 10% each hour. Write a function $P(t)$ for the population after $t$ hours. Write in the form $P(t)=a(1+r)^t$.