Caswell started studying how the number of branches on his tree grows over time. The relationship between the elapsed time ttt, in years, since Caswell started studying the tree, and the number of its branches, N(t)N(t)N, left parenthesis, t, right parenthesis, is modeled by the following function: N(t)=15⋅(1.64)t3.4 Complete the following sentence about the rate of change in the number of branches.