X = Xo + at, Y = Yo +bt, Z= Zo+ ct
Point (Xo, Yo, Zo) Direction vector= (a,b,c)
If they give you 2 points you can use the distnace formula for vectors (b1-a1, b2-a2, b3-a3) to find the direction vector and then use any of the two points to fill in the parametric or symmetric equation