add 4\sqrt{7}-10\sqrt{7}+7\sqrt{7}
\begin{aligned}
4\sqrt{7} - 10\sqrt{7} + 7\sqrt{7} &= (4 - 10 + 7)\sqrt{7}\\
&= 1\sqrt{7}\\
&= \sqrt{7}
\end{aligned}
4\sqrt{7} - 10\sqrt{7} + 7\sqrt{7} &= (4 - 10 + 7)\sqrt{7}\\
&= 1\sqrt{7}\\
&= \sqrt{7}
\end{aligned}