Your expression is:
4·⁴√(2x) + 6·⁴√(2x)
As you can see, the radicals are exactly the same: same index, same radicand.
Therefore you can treat it as if it was:
4 apples + 6 apples
which is 10 apples,
or in your case:
10·⁴√(2x)
Hence, the correct answer is option A.