17.) determine the intersection, if any, of the planes with the equations x+y-z+12=0 ansd 3x+4y=2z+8=0

18.) solve the following system of equations and give a geometrical interpretation of the result: x+y+z=6, 2x+y-3z=-5, 4x-5y+z=-3

19.) Give a geometrical interpretation of the intersection of the planes with the equations: x+y-3=0, y+z+5=0, x+z+2=0