I'm sure you know enough of the basic to solve this.
You just have to put it all together . . .
The line through the origin is normal to the plane
Find the point in which meets the plane
The plane has the normal vector: .
This is the direction vector of the line through the origin.
Its equations are: . . 
To find its intersection with the plane: . . 
. . substitute  into : .
Substitute into  and we have: .