Answer
$y=3$ or, in general form, $y-3=0$
Work Step by Step
Through $(1,3);$ slope $0$
Use the point-slope form of the equation of a line, which is $y-y_{1}=m(x-x_{1})$, where $(x_{1},y_{1})$ is a point through which the line passes and $m$ is the slope.
Both $(x_{1},y_{1})$ and $m$ are given. Substitute them into the formula and simplify to obtain the equation of this line:
$y-y_{1}=m(x-x_{1})$
$y-3=(0)(x-1)$
$y-3=0$
$y=3$ or, in general form, $y-3=0$
