Question

How do you simplify sqrt(8x)?

Answer 1

The answer is $2\sqrt{2x}$

You're right about the x in the root not being able to simplify, but that just means that the x stays inside the square root.  The 8 on the other hand simplifies to:
$\sqrt{4*2} =2 \sqrt{2}$

So this means that $\sqrt{8x} = 2\sqrt{2x}$