Write a program that computes and displays a 15 percent tip when the

Your question wasn't very clear, but I think I understand what you want. Additionally, you should really state what language you're working with. Here it is in C#, and shouldn't be too much of a hassle to translate in to other languages.

Console.Write("Enter payment: ");

float payment;

if (float.TryParse(Console.ReadLine(), out payment))
    Console.WriteLine((Math.Floor(payment * 100) / 100) * 0.15, + " at 15% tip.");
else
    Console.WriteLine("Invalid input.");

Copierighted lol boy need with his homework