Use a double Riemann sum, with $m=3$ intervals for $x$ and $n=4$ intervals for $y,$ sampling from the top$-$left U corner of each sub$-$rectangle, to approximate the value of the double integral $($round to $4$ decimal places$)$:

${\displaystyle \underset{2}{\overset{5}{}}}{\displaystyle \underset{1}{\overset{9}{}}}arctan(x^2+y^3)dydx$