combine. 3 square root 13 + 7 square root 13

3 squareroot(13) + 7 squareroot(13)

Note that you can only add or subtract terms with radicals if they have the same radicand (expression inside the radical sign) and same root (square root, cube root, fourth root, etc.)
Therefore, it becomes
= 10 squareroot(13)

Hope this helps~ :3