To solve something like this, keep in mind that the formula or format of a slope intercept equation is y=mx+b where m is the slope, b is the y intercept, and x and y are the values of the coordinate. To do this, plug your known values in the equation: -10=0(15)+b
Now that you have done that, you see that you have to solve for the value of b or the y intercept. To do this, first simplify the equation: -10=0+b
Then, since 0 times 15 simplifies to zero, you are left with your b value which is -10. Now that you have this information, you can now write your slope intercept equation as y=0x-10 or simply: y=-10