A contractor is preparing a bid to install swimming pools at a new housing addition. The estimated time to build the first pool is $36$ hours. The contractor estimates a $90$ percent learning rate.

a$.$ How long do you estimate the time required to install the second pool? $32\mathrm{.}4$ hours. $($Enter your response rounded to two decimal places.$)$

b$.$ How long do you estimate the time required to install the fourth pool? hours. $($Enter your response rounded to two decimal places.$)$