Length=width+5 feet.
Diagonal=√(length²+width²)=12 ft.
So diagonal²=144 and (width+5)²+width²=144.
Use w for width.
w²+10w+25+w²=144, 2w²+10w-119=0.
Use the formula to solve the quadratic:
w=(-10±√(100+952))/4=(-10±√1052)/4=5.6ft to the nearest tenth of a foot.
The length is 5ft longer=10.6ft.