Satoshi started studying how the number of branches on his tree grows over time.
The relationship between the elapsed time $t$, in years, since Satoshi started studying the tree, and the number of its branches, $N(t)$, is modeled by the following function:
###$N(t)=24\cdot 3\^{\Large \frac{t}{15}}$
**Complete the following sentence about the growth rate of the branches.**
The number of branches triples every [[☃ numeric-input 1]] years.