Answer
$f(28)=5$
$f(4)=1$
$f(3)=0$
$f(-1)=$ Not a real number.
Work Step by Step
The given function is
$f(x)=\sqrt{x−3}$
Plug x=28 into the function.
$f(28)=\sqrt{28−3}$
Simplify.
$f(28)=\sqrt{25}$
$f(28)=\sqrt{5^2}$
$f(28)=5$
Plug x=4 into the function.
$f(4)=\sqrt{4−3}$
Simplify.
$f(4)=\sqrt{1}$
$f(4)=\sqrt{1^2}$
$f(4)=1$
Plug x=3 into the function.
$f(3)=\sqrt{3−3}$
Simplify.
$f(3)=\sqrt{0}$
$f(3)=0$
Plug x=-1 into the function.
$f(-1)=\sqrt{-1-3}$
Simplify.
$f(-1)=\sqrt{-4}$
Not a real number.