Let us suppose the width is x feet
the length is given 12 feet
Perimeter of teh garden = 2( Length + width )= 2( 12+ x)
Fencing required = perimeter of garden
36 = 2( 12+x)
36 = 2*12 + 2x
36 = 24 + 2x
36-24 = 2x
12 = 2x
12/2 = x
6 = x
Width = x feet = 6 feet .Answer .