An initial population of 4 tribbles was brought aboard the Enterprise. They grow at a...

An exponential growth function is of the form ${\displaystyle y=a{\left(b\right)}^x}$ where aa is the initial amount and bb is the growth factor.
If the initial population is 4 tribbles, then a=4.
If the population is growing at a rate of 50% every hour, then the growth factor is b=100%+50%=150%=1.5.
The exponential growth function is then y=4(1.5)x.