it's good to write it out
length = 5 + width
area = 150
width = x
length = 5 + x
area = length * width
so
(5 + x) (x) = 150
5x + x^2 = 150
x^2 + 5x - 150 = 0
following you have to guess what 2 numbers when multiplied male 150 and when added make 5
and they are 15 and 10
(x +15) (x-10)
x = -15
x = 10
so the dimensions are
length = 15
and
width = 10
