Multiply the numbers that are OUTSIDE the square root and keep them OUTSIDE the square root, and multiply the numbers that are INSIDE the square root and keep them INSIDE the square root:
For more detailed explanation of radicals see my Lesson Plans about Square Roots in algebra.com, or go to my website (click on my tutor name "Rapaljer" anywhere in algebra.com!), and look for "Basic Algebra", then "Samples from Basic Algebra: One Step at a Time," then Chapter 5 Radicals, Section 5.04 Multiplication of Radicals. See also my "Math in Living Color" page, "Basic Algebra," "Chapter 5." I hope you will find this helpful.