Let w be the width. Then your equation is w*(w+8) = (w+4)*((w+8)-5), or, which is the same, w*(w+8) = (w+4)*(w+3), w^2 + 8w = w^2 + 4w + 3w + 12, w = 12. Check. 12*(12+8) = 240. (12+4)(12+3) = 16*15 = 240. ! Correct ! Answer. the original dimensions of the rectangle are 12 x 8 cm.