A would be 6/12 (1/2) and B would be 1/12. To make this easier to understand, think of it this way. 6+1=7, and 6-1=5. In the future, find what adds to 7 and begin plugging in numbers until you get the correct answer.
They each contributed $6.75. I got that because i divided the $27.00 by the 4 friends and got $6.75, to make sure I also multiplied the $6.75 by 4 and got $27.00
