Fred started studying how the number of branches on his tree grows over time. The relationship between the labs time t in years since Fred started studying the tree in the number of its branches B year(t), is modeled by the following function:

Byear(t)=20•(2.5)^t

Complete the following sentence about the monthly rate of change in the number of branches. Round your answer to two decimal places.

Every month the number of branches increases by a factor of _.