We are given 4 choices for x and we have to choose the one whose value lies between 11 and 12. To do that, we need to know what each square root evaluates to.
Now, we must remember the squares of integers:
10^2 = 100
11^2 = 121
12^2 = 144
13^2 = 169
14^2 = 196
Therefore, we could go the other way around and say
√100 = 10
√121 = 11
√144 = 12
√169 = 13
√196 = 14
Now back to our question but phrased in another way:
Which of the choices lies between 144 and 121?
The answer is 136; therefore, the correct choice is A.