Change of Variables & the Jacobian · Medium problem

A fabric is cut in two stages: first a stretch $(u,v)\mapsto(p,q)=(2u,3v)$, then a shear $(p,q)\mapsto(x,y)=(p+q,p-q)$. A swatch of area $4$ in $(u,v)$-space is cut out. Since Jacobians of composed maps multiply, find the area of the corresponding piece of fabric in $(x,y)$.