What is the sum of the two numbers a and B, and what is the difference between them

What is the sum of the two numbers a and B, and what is the difference between them

4 / 7 + 5 / 11 = 44 / 77 + 35 / 77 = 79 / 77
4 / 7-5 / 11 = 44 / 77-35 / 77 = 9 / 77