15. Find a vector normal to the plane $2x - 3y + z = 15$.
16. Which of the following statements is true for the lines $(1, 1, 1) + t(1, 2, -1)$ and $(3, 2, 1) + t(-1, -5, 3)$
A. The two lines are parallel
B. The two lines intersect
C. Neither A. nor B. is true.