Question: Given the lines

\[\begin{aligned} & \mathbf{x}=\left( 1,2,-1 \right)+t\left( 3,1,2 \right) \\ & \mathbf{y}=\left( 9,0,1 \right)+s\left( -1,2,1 \right) \\ \end{aligned}\]

(a) Determine whether they intersect.

(b) If they intersect find the equation of the plane determined by the lines.