The Length Of A Rectangle Is 8 Cm Greater Than Its Width. Find The Dimensions Of The Rectangle If Its Area Is 105cm2?

A = l * w    (definition)
l = w + 8    (define length)

A = (w + 8) * w   (substitute l with w+8)
105 = (w + 8) * w  (substitute A with 105)
105 = w * w + 8w  (multiply both terms w+8 with w)

w * 2 + 8 * w - 105 = 0 (move 105 to other side)

Now you can use the a b c formula (a = 1, b = 8 c = -105) to find the solutions to w
You will find the answers -15 and 7. -15 is not valid, since with has to be larger then 0.

w = 7. (abc-formula)
l = w + 8 = 7 + 8 = 15 (substitute w with 7)

l = 15, w = 7.
15 * 7 = 105    (check the answer)