Is there another shortcut?

In the last question, where we are asked to find the value of a, given these huge numbers to multiply, I found out that when you multiply 81 by 4, the answer is 324, which is 12 squared. 36, obviously, is the 6 squared. It there a shortcut to find the square root of this BIG number given that we already found out 2 perfect squares?

@ingeniousnewt 12 squared is 144, and 18 squared is 324