Va = (-2;1;1), Vb = (1;5;0), Vc = (4;4;-2), PRvc = (3a - 2b) - ?

Answer 1

3(-2,1,1) = (-6,3,3)
2(1,5,0) = (3,10,0)
So you want
(-9,-7,3) - (x,y,z) = (4,4,-2)
Now just solve for x,y,z