$1).$Find the linear approximation to the equation $f(x,y)=5\sqrt[\phantom{2}]{\frac{xy}{3}}$ at the point $(6,2,10),$ and use it to approximate $f(6\mathrm{.}11,2\mathrm{.}21)$

$f(6\mathrm{.}11,2\mathrm{.}21)$~$=$

$$

Make sure your answer is accurate to at least three decimal places, or give an exact answer.

$2).$Use linear approximation to approximate $\frac{\sqrt[\phantom{2}]{22}}{0\mathrm{.}97}.($Use a function of two variables.$)$