A good answer might be:
d = ( -12.4, 14.8, 0.0 )T
e = ( 6.2, -10.2, 17.0 )T
f = ( 6.2, -4.6, -17.0 )T
----------------------
( 0.0, 0.0 0.0 )T
QUESTION 13:
Find x, y, and z so that the following is true:
a = ( 8.6, 7.4, 3.9 )
b = ( 4.2, 2.2, -3.0 )
c = ( x, y, z )
a + b + c = 0