Explanation:
6z=126
z = 126 ÷ 6 = 21
Chris's
z = 756
6z= 126
z = 126 × 6 = 756
correct answer = 21
the number 6 is being multiplied with z.So if the number 6 is going to the right side it will divide the number on the right side.
but for chris he multiplied the number on the right side with 6.So that is the mistake.