12 can be written as 2^2 * 3, so, seeing the 2^2, we can take the 2 out of the square root.
Now, we have 10 * sqrt (3xm^3)
Looking at the m^3, we see that it can also be written as m^2 * m, so we can take an m from the square root:
10m * sqrt(3xm)
As there are no more perfect squares inside the root that we can take out, our answer is (D).
