The average return for large$-$cap domestic stock funds over three years was $.$ Assume the three$-$year returns were normally distributed across funds with a standard deviation of $.$

a$.$ What is the probability an individual large$-$cap domestic stock fund had a three$-$year return of at least $20\%($to $4$ decimals$)?$

b$.$ What is the probability an individual large$-$cap domestic stock fund had a three$-$year return of $10\%$ or less $($to $4$ decimals$)?$

c$.$ How big does the return have to be to put a domestic stock fund in the top $10\%$ for the three$-$year period $($to $2$ decimals$)?$