How do you set up the problem 4 times the square root of x less than 20?

Do it exactly as the question directs:

Four times means you're multiplying SOMETHING by four, so go ahead and write a four down:

4

Times the square root of means you're multiplying 4 by the square root of SOMETHING, so go ahead and put that radical next to the four:

(note that there is no radical sign on here, but x^(1/2) is the same thing as the square root of x, sooo):

4(SOMETHING^(1/2))

Now it tells us that SOMETHING is x less than 20, which means you're subtracting 20 by x, or:

SOMETHING = 20-x.

SO, putting 20-x instead of something into the expression leave us with:

4((20-x)^(1/2))

or, "four times radical twenty minus x."

Hope that helps a little.