Answer
Domain: $\frac{4}{5}\geq x.$
At $-1$: $3$
Work Step by Step
We plug in $x=-1$ to $f(x)$ to get $f(-1)=\sqrt{4-5\cdot(-1)}=\sqrt{4-(-5)}=\sqrt9=3.$
We know that the square root function is undefined for negative numbers, hence $4-5x\geq0\\4\geq5x\\\frac{4}{5}\geq x.$
