$($a$)$ What is the average useful power output $($in W $)$ of a person who does $5\mathrm{.}00{10}^{6}J$ of useful work in $8\mathrm{.}40$ h $?$

w

$($b$)$ Working at this rate, how long $($in s$)$ will it take this person to lift $1700$ kg of bricks $1\mathrm{.}60$ m to a platform? $($Work done to lift his body can be omitted because it is not considered useful output here.$)$

s