Square root of 300a to the power of 7

The answer should be

Since it's a square root (2) the numbers need to be in groups of two, in order for the numbers to be taken outside the root they need to be the same number. Since there was only one 3, no pair could be made and it stayed inside the root. There was 1 a left over after the rest were put into a group. The reason the a is the only one with a power is because there were 3 groups of a instead of one, as compared to the 2 and 5.