Square root of (36*45+18*72)

Hello. For the below equation, I factored out 9 as follows. Why is this incorrect? \(\sqrt36*45+18*72\) \(\sqrt9(4*5+2*8)\) \(\sqrt9(36)\) 3*6 18 The correct answer is 54. Thanks!

https://gmatclub.com/forum/square-root-of-317708.html