Question 824351
(x+3)^2 = x^2 + 45


x^2 + 6x + 9 = x^2 + 45


x^2 + 6x + 9 - x^2 = 45


6x + 9 = 45


6x = 45 - 9


6x = 36


x = 36/6


x = 6


The side length of the original square is <font color="red">6 cm</font>