Can someone explain how to simplify square roots with variables and eexponents in them? ? i'd also be if you explained step-by-step how to
solve (16x^4)^3/2 and how to simplify 3y^4/3 times 3yx^1/2? i have to do a retake on my math test and i really need !

X^a/b is   . The way I memorise that is x^1/3 is the cubic root of x. Do you get it? In that case, x is raised to a power of 1 and the cubic root is practically has a power of 3.
In your example, 

is practically square rooting each term then cubing them individually. Remember when square-rooting any index you halve it. I'll elaborate:

= 
= 4
Then cube each,
= 64 
and  = 

As for the 2nd part: you must use the rules of indices.

So breaking the question up:

3 * 3 = 9
stays as is since the 2nd term does not contain x
now: 

This makes your final answer look like this:


I hope that helped and good luck in your test!