Set each piece = to 56, assuming that the 2 variables for which you are not solving are each equal to 0.
7x -2(0)-14(0) = 56
7x=56 (divide each side by 7)
X = ?
(__, 0, 0)
7(0) - 2y - 14 (0) = 56
-2y = 56 (divide each side by -2)
Y= ?
(0, __ , 0)
7(0) - 2(0) - 14z = 56
-14z = 56 (divide each side by -14)
z = ?
(0, 0, __)