Mr. lee listed 6/8,3/4, and 10/12 on the board and said these were all equivalent fractions. Do u agree or disagree with Mr. Lee? why

No, the fractions are not equivalent because they are not equal to each other.

6/8 and 3/4 are equal to each other, but 10/12 is not. If he had written 6/8, 3/4 and 9/12 then they would all be equal because 3/4 by 3 (to get a denominator of 12) would be 9/12. 10/12 can not be equal to these, but 3/4 to get a denominator of 8 would be times 2, and equal to 6/8.

So ... 6/8 and 3/4 is equal. 10/12 is not.