Without using a calculator I would say the root is between 10 and 11
How I found the answer:
I know 10 * 10 = 100
I know 11 * 11 = 121
So the root of 100 = 10 and the root of 121 = 11 so that means the root of 108 is somewhere between 10 and 11, which the root of 108 = 10.3923