What don't you understand? Personally, the phrase "scalar equation for the plane" confused me until I realized the scalar equation for a plane is an equation for a plane in the same form as both and .
Determine a scalar equation for the plane that passes through the point (2, 0, −1) and is perpendicular to the line of intersection of the planes
2x + y – z + 5 = 0 and x + y + 2z + 7 = 0.