B and C together can do a certain work in one-third of the time in which A
alone can do it, whereas A and B together can do the same work in half
the time in which C alone can do it. If B alone can do the work in 28
days, then how long will A and C together take to do it?At least one detailed Approach

1) 15
2) 20
3) 12.5
4) CBD