Answer:
Somewhere between 12 and 13, perhaps 12.25
Explanation:
This is a (rather) simple explanation:
Look for 2 square numbers that are either side of 150
In this case, it is 144 and 169
The square root of 144 is 12 and the square root of 169 is 13
Therefore we can estimate that the square root of 150 is somewhere between 12 and 13.
As 150 is a lot closer to 144 to 169, I would estimate around 12.25 but you do not need an exact value :)