We have to find the equation of a line in the slope-intercept form. We remember that it is given by:
[tex]y=mx+b[/tex]where m represents the slope, and b the y-intercept.
In this exercise, we are given the slope:
[tex]m=0[/tex]And that it passes through the point (-15,12). Replacing the slope onto the general form, and using the point, we get:
[tex]\begin{gathered} 12=0(-15)+b \\ 12=0+b \\ 12=b \end{gathered}[/tex]And thus, its y-intercept is 12. This means that the equation in the slope-form is given by:
[tex]\begin{gathered} y=0x+12 \\ y=12 \end{gathered}[/tex]