`|4-sqrt7|-|1-3sqrt7| \ \ \ stackrel(sqrt7 `|4-sqrt7|-|1-3sqrt7| \ \ \ stackrel(sqrt7

$=4-\sqrt{7}-\left(-\left(1-3\sqrt{7}\right)\right)=4-\sqrt{7}+1-3\sqrt{7}=\underline{\underline{5-4\sqrt{7}}}$