Well if he owes $45 and has 5 friends offering, you would just need to divide. So 45/5 is 9. So each of his friends owe $9. Or if he and his friends are paying/splitting it then it would be 45/6 which is 7.5, so he and his friends would all owe $7.50. But I don’t know if he and friends are paying or just friends. Hope this helps