In the end, each had 144/3 = 48 erasers
So Charlie had 24 erasers before getting 24 from Bill
And Bill must have had ( 48 + 24) = 72 erasers before he gave some to Charlie
So.....Bill must have had 36 erasers to start out
Then Alan must have started out with 48 + 36 = 84 erasers
Proof
Alan starts with 84 and gives away 36 = he has 48 in the end
Bill starts with 36 gets 36 from Alan and gives away 24 = 36 + 36 - 24 = he has 48 in the end
Charlie starts out with 24 and ends up with twice this = 48