Q$7)$ The daily water levels $($normalized to the respective full condition$)$ of two reservoirs

A and $B$ are denoted by two random variables $x$ and $Y$ having the following joint PDF:

$f(x,y)=(x^2+y),0$

$(a)$ Determine the marginal density function $of$ the daily water level for reservoir

$A.$

$(b)If$ reservoir $Ais$ half full $on$ a given day, what $is$ the probability that the water

level will $be$ more than half full?