Well, this should be simpler than they are making it.
Point slope form is y - y1 = m(x - x1). Since our given point is (0,0), we have...
y - 0 = (3/8)(x - 0)
y = (3/8)x
That's it. In math, our final answer doesn't include things like + 0 or - 0, because that would be like calling you Dru'Londa + 0, though that might be a cool nickname.