Nice job with code tags.
Problem is that randnum is an integer variable, but advertisingcost (without parentheses!!!) is a function object. So error message simply tells you that you can't multiply integer and a function (you don't say?! :P).
What you probably want instead of advertisingcost is the value that the function returns. For that, you will need to call that function (function name with parenthses) and modify that function, so it returns the value you want to include in calculation. I see you did that in your other functions.
Problem is that randnum is an integer variable, but advertisingcost (without parentheses!!!) is a function object. So error message simply tells you that you can't multiply integer and a function (you don't say?! :P).
What you probably want instead of advertisingcost is the value that the function returns. For that, you will need to call that function (function name with parenthses) and modify that function, so it returns the value you want to include in calculation. I see you did that in your other functions.