"Programming in Python" fails to solve the problem?

Question

Python

"Write a Generous Visitor program that allows the user to enter the amount of
a restaurant bill. The program should output two values: a 15% tip and a 20% tip."
Sorry for the stupid question.
Please point out the mistake and, if possible, chew it.

#Программа считает сколько чаевых вы должны оставить.
many = int(input("Введите сумму вашего счета"))
ch1 = many / 100 * 15
ch2 = many / 100 * 20
print("Общая сумма = ". ch1)
print("Общая сумма = ". ch2)
input("\n\nНажмите Enter, чтобы выйти")

Answer 1

print("Общая сумма = ", ch1)
print("Общая сумма = ", ch2)

There should be commas, not periods

Answer 2

If I smoked 3.5 correctly

print ('Общая сума: {0!s}'.format(many / 100 * 15))