subtract 10 radical 7 - 4 radical 7

To simplify \( 10\sqrt{7} - 4\sqrt{7} \), we combine like terms:

\[ 10\sqrt{7} - 4\sqrt{7} = (10 - 4)\sqrt{7} = 6\sqrt{7} \]

So the answer is \( 6\sqrt{7} \).

The correct choice is:

D. 6 radical 7