You find a certain stock that had returns of $10$ percent, $15$ percent, $22$ percent, and $18$ percent for four of the last five years. The average return of the stock over this period was $9\mathrm{.}64$ percent.

a$.$

What was the stock$$s return for the missing year? $($Do not round intermediate calculations and enter your answer as a percent rounded to $1$ decimal place, e$.$g$.,32\mathrm{.}1.)$

b$.$ What is the standard deviation of the stock$$s returns? $($Do not round intermediate calculations and enter your answer as a percent rounded to $2$ decimal places, e$.$g$.,32\mathrm{.}16.)$