$(1$ point$)$ Find positive numbers a and $b$ so that the change of variables $s=ax,t=by$ transforms the integral ${}_{R}dxdy$ into

${}_T|\frac{\text{d}\text{e}\text{l}(x,y)}{\text{d}\text{e}\text{l}(s,t)}|dsdt$

for the region $R,$ the elliptical region $\frac{x^2}{4}+\frac{y^2}{9}1$ and the region $T,$ the circle $s^2+t^2=1.$

$a=$

$b=$

What is $|\frac{\text{d}\text{e}\text{l}(x,y)}{\text{d}\text{e}\text{l}(s.t)}|$ in this case?

$|\frac{\text{d}\text{e}\text{l}(x,y)}{\text{d}\text{e}\text{l}(s,t)}|=$