This could be done in two different ways. One is by first knowing the perimeter of rectangle, which in this case is 70, then identifying the increase of the opposite side, increased by 5 which is equal to 10 overall. After that let us establish a working equation, square = rectangle - 10. By that let us substitute the value, square = 70 - 10; square = 60 cm. Then remember that square has four equal side, so square = 60 divided by 4 = 15. So the original side of square is 15 cm.