## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

We know that the area of a rectangle is given by: $$A=lw$$ Thus, we find: $$40=w(w+6) \\ w^2+6w-40=0 \\ w\left(w-4\right)+10\left(w-4\right)=0 \\ \left(w-4\right)\left(w+10\right)=0 \\ w=4 \\ l=4+6=10$$