The best statement that describes Gary’s error is:
Gary did not use two equivalent expressions in the equation.
This is because while he correctly factored out a common factor of 3, the expressions inside the parentheses (22 + 12) do not equal the original numbers (66 and 36). The correct expression using the distributive property should have used the greatest common factor (which is 6) in combination with the correct remaining expressions (which would lead to \( 6 (11 + 6) \) instead).