Answer :
The equation of a line is given by:
[tex]y-y_1=m(x-x_1)[/tex]where (x1,y1) is a point on the line and m is the slope.
The slope is given by:
[tex]m=\frac{y_2-y_1}{x_2-x_1}[/tex]Then, in this case:
[tex]\begin{gathered} m=\frac{9-9}{-2-15} \\ =\frac{0}{-17} \\ =0 \end{gathered}[/tex]Once we have the slope we can plug the values in our first equation:
[tex]\begin{gathered} y-9=0(x-15) \\ y-9=0 \\ y=9 \end{gathered}[/tex]Therefore the equation of the line we are lookinfg for is y=9.