Given $\displaystyle f(x) = \frac{3}{x}$

Is it gonna be $\displaystyle f(x+h) = \frac{3}{x} + h$

or

$\displaystyle f(x+h)=\frac{3}{x+h}$

another question

Given $\displaystyle G(x) = \sqrt{4-x}$

is it gonna be $\displaystyle G(x+h) = \sqrt{4-x+h}$ or $\displaystyle \sqrt{4-x} + h?$