a) x + 3y - 3z = x + 2y + y - 3z = 17 + 4 = 21
b) 2x + 5y - 3z = 2x + 4y +y - 3z = 2 (x + 2y) + y - 3z = 2· 17 + 4 = 38
c) (3x+6y) + (2y -6z) = 3(x+2y) + 2(y -3z) = 17·3 + 2·4 = 59
d) (2x+4y) · (x+4y-6z) = 2(x+2y) · (x+2y +2(y-3z)) = (2·17) · (17 +2·4) = 850