2a+2b=72
a+b=36
a=36-b
P=ah
P=a*h_1=b*h_2
\frac{h_2}{h_1}=\frac{3}{1}
\left \{ {{1a=3b} \atop {a=36-b}} \right.
\left \{ {{36-b=3b} \atop {a=36-b}} \right.
\left \{ {{-2b=-36} \atop {a=36-b}} \right.
\left \{ {{b=18} \atop {a=36-18}} \right.
\left \{ {{b=18} \atop {a=18}} \right.