Needham Multivariable Calculus: Write Equation of a Plane

Here is a weird iteration of an equation-of-a-plane problem. Instead of knowing a point and a normal vector, we know a line that it contains and a parallel plane. But knowing the parallel plane gives us the normal vector for free (think about why!), and knowing a line contained by the plane can be used to give us a *point*, which is what we really want. This is the case with tons of problems in Multivariable - the type of info you "really" need is buried somewhere, and you just have to go and find it.