Arectangular flower bed covers an area of 11.76 square feet in the garden. the width of the flower bed is 3.5 feet less than its length.

The length and width of the garden will be obtain as follows:
let the length be x ft, the width will be (x+3.5)ft
area of the bed will be:
A=length*width
11.76=x(x+3.5)
11.76=x^2+3.5x
thus
x^2+3.5x-11.76=0
solving this by quadratic formula we get:
x=[-b+/-sqrt(b^2-4ac)]/2a
thus plugging in the values we obtain
x=[-3.5+/-sqrt(3.5^2-4(-11.76*1))]/2
x=[-3.5+/-sqrt59.29]/2
x=[-3.5+/-7.7]/2
x=4.2 or -11.2
thus the length will be x=4.2 ft and the width will be x-3.5=0.7 ft