Hi Bubble,
You figure the percentage by dividing the amount paid by the bill and multiplying by 100.
For example, (322.70/839.21)(100)
For the next part of the question, you subtract the amount that the generous person pays from the bill
839.21 - 392
Then convert the percentages that you calculated in part 1 to decimals by moving the decimal points two places to the left (same as dividing the percentages by 100) and multiply them times the new monthly bill that you found by subtracting 392 from the old bill. This will give you the new amounts that each person will pay.
Have fun.
Dan
Bubble G.
01/13/16