What is the simplest form of square root of

First you simplify the fraction and variables inside the root. Reduce 126/32 and use exponent rules for dividing variables(subtract the exponents). This will give you,

Then move onto the root. Using radical properties you take the root of the numerator and denominator seperately. Since the root of the numerator is not a rational number or perfect square it stays as,

Altogether the new equation will be this,

You can still simplify this further by reducing the radical in the numerator.
You prime factor it to give you 7×9 = 63 which lets you factor out a 3. You can also factor out 4 of the y variables. Breaking down the numerator you get this.

Which simplifies to,

Your final simplest form equation is,