Width - x ft.
Length - (x+6)ft.
x(x+6)=315
x²+6x-315=0
a=1, b=6, c=-315
D=b²-4ac=36+4*1*315=1296, √D=√1296=36
[tex] x = \frac{-b+/- \sqrt{D} }{2a}
\\ \\ x= \frac{-6+/-36}{2}
\\ \\ x=15, x=-21[/tex]
For the width we can use only positive number.
The width =15 ft.
The length =15+6=21 ft.
Check :
Area =15*21=315 ft²
