please help!

The width of a rectangle is 4ft less than the length. The area is 12 ft sq. Find the length and the width.

with : x

length : x+4

x(x+4) = 12
x^2 + 4x - 12 = 0
(x+6)(x-2) = 0
x = -6 or x = 2
but clearly x has to be positive

so the width is 2 and the length is 6

check: what is 2 times 6 ?