The answer is A, if four people can fit into 1 carriage, then you'll need 5.5 carriages, but you can't have a half of a carriage so you'll round up to an even 6
You dont need the percentage of tip. to calculate the bill, divide 100 by 15, then multiply that number by 1.65, you will get the total of the bill afer tax. if you add 1.65 to the total you get the total after tax and tip