Mathematics isn't really something I'm good at but luckily, Python makes it easy when using functions. I'm also using .format to correctly show decimal places - as well as # -*- coding: utf-8 -*- so that Python can print currency symbols..

# -*- coding: utf-8 -*-
def add(a, b, c):
    print "\nADDING %d + %d + %d" % (a, b, c)
    return a + b + c

price = add(12, 12, 12);print "The price is £{0:.2f}\n".format (price)

def multiply(a, b):
    print "MULTIPLYING %d * %d" % (a, b)
    return a * b

multiply_price = multiply(10, 10);print "The price is £{0:.2f}\n".format (multiply_price)

def subtracting(a, b):
    print "SUBTRACTING %d - %d" % (a, b)
    return a - b

subtract_price = subtracting(100, 50);print "The price is £{0:.2f}\n".format (subtract_price)

def division(a, b):
    print "DIVIDING %d / %d" % (a, b)
    return a / b

division_price = division(90, 2);print "The price is £{0:.2f}\n".format (division_price)