basically, it is when legnth is

the width
legnth=12
legnth=

times width
12=

times width
multiply both sides by 2
24=

times width
subtract 1
23=√5 times width
divide both sides by √5
23/(√5)=width
multiply by (√5)/(√5) to rationalize denomenator

=width
aprox 10.28 so 10.3 ft
w=

ft or aprox 10.3ft