After simplify the 6/9, it should be 2/3.
After simplify the 16/24,it should be 2/3.
After simplify the 12/21,it should be 4/7.
After simplify the 8/12,it should be 2/3.
After simplify the 8/20,it should be 2/5.
After simplify the 4/8,it should be 1/2.
After simplify the 6/7,it should be 6/7.
After simplify the 5/18,it should be 15/18.