#### Answer

$\sqrt 35xt$

#### Work Step by Step

The product rule for radicals tells us that $\sqrt[n] a\times\sqrt[n] b=\sqrt[n] ab$ (when $\sqrt[n] a$ and $\sqrt[n] b$ are real numbers and $n$ is a natural number). That is, the product of two nth roots is the nth root of the product.
Therefore, $\sqrt 7\times\sqrt 5xt=\sqrt (7\times 5xt)=\sqrt 35xt$.