I'm pretty sure 10/63 is simplified.
You want to be finding out what two factors (where one of them is a perfect square) has the produce of 63. It seems like 9 x 7 (9 is the perfect square) works.

The square root of 9 is 3 so we can just have

(which just means 3 times the square root of 7).
To solve for a, you must get a by itself on one side of the equation. Now, a is "joined" to m by multiplication. To "separate" them, use the inverse operation, division.
Divide both sides of the equation by m.