Three lines $L\_1,L\_2,L\_3$ pass through the origin with the parallel vectors $$V\_1=i+2j-k$$$$V\_2=3i+5j+7k$$$$V\_3=2i+3j+8k$$ are given,show that the lines are all in a plane and find the equation of the plane.

The parametric equation of the lines :

$$x\_1=t,y\_1=2t,z\_1=-t$$
$$x\_2=3t,y\_2=5t,z\_2=7t$$
$$x\_3=2t,y\_3=3t,z\_3=8t$$

But I don't know how to continue.