A $45-$in$.$ vertical jump consists of two parts. The first stage is the quick acceleration of the center of mass from a crouching to a standing position. The center of mass rises by $20$ cm in this stage. In the second stage, the players feet leave the floor and the center of mass rises $45$ in$.$ under the influence of gravity alone. 

 What is the average acceleration during the first phase of the jump? $($Round the final answer to two decimal places.$)$  answer in ft$/$s$\mathrm{²}$