How do I add a button in a Tip Calculator android app that allows the user to input the number of guests and calculates the tip and total per guest? The app looks like the image above. I have all the code for that, I'm only lacking the guest number and split the bill part. Android Programming only.

.4 31%A 21:12 4G Tip Calculator Total Bill Tip Percent Split Number Total amount to pay Total amount of tip to pay Calculate Tip