The first equation is correct: 3/4 is equal to 15/20.
The second equation is incorrect: 7:5 is not equal to 77/55.
The third equation is incorrect: 12/18 is not equal to 14/21.
The first equation is correct: 3/4 is equal to 15/20.
The second equation is incorrect: 7:5 is not equal to 77/55.
The third equation is incorrect: 12/18 is not equal to 14/21.