# How do you simplify 4sqrt(20)-sqrt(45)+7sqrt5?

First, you need to properly factor all of your roots. This starts with the $4 \sqrt{20}$ where you must factor out a 2, leaving $8 \sqrt{5}$. Then on the $\sqrt{45}$ factor out a 3, leaving $3 \sqrt{5}$. Now you are left with $8 \sqrt{5} - 3 \sqrt{5} + 7 \sqrt{5}$. By combining like terms you have $12 \sqrt{5}$