Question 465604
Let x = width of the rectangle
x + 15= the length of the rectangle

(x+3)(x+15-5) = x(x+15) + 20
x^2+10x+3x+30 = x^2+15x+20
30-20 = 15x-10x-3x
2x = 10
x = 5
x+15 = 5+15 = 20

The dimension of original rectangle are:
width = 5 cm.
length = 20 cm.