A and B working together, can do a piece of work in $4\frac{1}{2}$ hours, B and C working together can do it in 3 hours, C and A working together can do it in $2\frac{1}{4}$ hours. All of them begin the work at the same time. find how much time they will take to finish the piece of work.
1). 3 hours
2). 2 hours
3). 2.5 hours
4). 3.25 hours