All solutions here are SUGGESTED. Mr. Teng will hold no liability for any errors. Comments are entirely personal opinions.
Direction vector of
Normal vector of
Since is parallel to the normal vector of is perpendicular to .
Point of intersection .
Since satisfies all 3 equations, A lies on l.
Since is the midpoint of A & B, by ratio theorem,
to the nearest whole number.
Students must give answers in coordinates, rather than as a position vector.