#### Answer

4800 foxes

#### Work Step by Step

You have f(x)=75 $\times$ $4^{x}$.Where it represents the number of foxes after 15-year periods. Plug in x=3 since there are 3 15-year periods in 45 years.
f(3)=75 $\times$ $4^{3}$
f(3)=4800
After 45 years, there would be 4800 foxes.