Mark is solving the following system. X+Y+Z = 2
(1)
(2)
3x+2y+Z = 8
4x-y-72 = 16
(3)
Step 1: He multiplies equation (1) by 7 and adds it to equation (3).
Step 2: He multiplies equation (3) by 2 and adds it to equation (2).
Which statement explains Mark's mistake?
O He added equation (3) instead of equation (2) in step 1.
O He did not multiply equation (3) by the same number as equation (1).
O He did not eliminate the same variables in steps 1 and 2.
O He added equation the equations in step instead of subtracting them.

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