[Fyron]

By 'distance' I meant we didn't take into account position. That wasn't worded well.

Yes we did; the very definition of intercepting a target object is when the positions are equal. We have two position equations, with two unknowns (time and position). Since we know the positions must be equal, we can simply substitute one of the equations for the S value (position) in the other equation, thus eliminating it.

So I should make two formulas, one with a '+' there and the other with a '-' there and if one returns a zero, I use the other?

No... both will return zeros of the quadratic function (aka x-intercepts). I wasn't talking about the integer value 0. A negative zero/intercept is thrown out, as per previous post.