Answer
$y=7$ or, in general form, $y-7=0$
Work Step by Step
Through $(1,7)$ and $(4,7)$
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.
Two points through which the line passes are given. Use them to find the slope of the line:
$m=\dfrac{y_{2}-y_{1}}{x_{2}-x_{1}}=\dfrac{7-7}{4-1}=\dfrac{0}{3}=0$
Substitute $m$ and whichever of the points given into the formula to obtain the equation of this line:
$y-y_{1}=m(x-x_{1})$
$y-7=(0)(x-1)$
$y-7=0$
$y=7$ or, in general form, $y-7=0$