jmc

We see that $(2x+3y{)}^2=(4x^2+9y^2)+12xy=4$. We want to find $4x^2+9y^2$ and are given $xy=-5$. So, $4x^2+9y^2+12xy=4x^2+9y^2+12(-5)=4$. It follows that $4x^2+9y^2=\boxed{64}$.