21odunayo
1

# area of room is 320 and width is 4/5 of length

Area is w*l and $w=\frac{4l}5$, thus the area is $\frac{4l^2}5$. Make it equal to 320 and you get $l^2=400$, thus $l=\pm{20}$, the minus one not being meaningful in our context. Thus the length is 20, while the width is 16.