Answer:
I think 0.15b would be a no because that is just what a customer would tip.
15b is also a no because that is 15 times the price of the bill.
b + 0.15b is a yes because you are adding the bill and 15% of the bill as a tip.
1.15b is a no because you are multiplying the bill by 1.15.
1.015 is a no because you're multiplying the bill by 1.015.
b + (15/100)b is a yes because you are adding the bill and 15% out of 100% of the bill as a tip.
b + 0.15 is a no because you would be tipping them 15 cents, not 15% of the bill.