Answer
$y=-x+3$
Work Step by Step
Using $y-y_1=\dfrac{y_1-y_2}{x_1-x_2}(x-x_1)$ or the Two-Point Form of linear equations, where
\begin{array}{l}\require{cancel}
x_1=
0
,\\x_2=
-1
,\\y_1=
3
,\\y_2=
4
,\end{array}
the equation of the line is
\begin{array}{l}\require{cancel}
y-3=\dfrac{3-4}{0-(-1)}(x-0)
\\\\
y-3=\dfrac{3-4}{0+1}(x-0)
\\\\
y-3=\dfrac{-1}{1}(x)
\\\\
y-3=-x
.\end{array}
In $y=mx+b$ or the Slope-Intercept Form, the equation above is equivalent to
\begin{array}{l}\require{cancel}
y-3=-x
\\\\
y=-x+3
.\end{array}