So first you want the radicals to have a similar number inside the radical. So radical 20 would be radical 4 times radical 5. You could even simplify it more so the final simplified answer of radical 20 would be 2 radical 5. so then for radical 80, you could do radical 16 times radical 5. since 16 is a perfect square you could make it 4. so the simplified version would be 4 radical 5. Since both of them have a common number inside the radical, you can add them now. the answer would be B. Hope this helps!