# Optimization problem - maximizing variables

I am trying to solve the mail in advertisement problem. I have 4 variables: customers (number of customers per day, for example 2, 4, 10, etc.; the higher the number, the better), budget(total daily budget for total number of daily customers, $$5,$$50, $250, etc.; the lower the number, the better), ready_to_buy (customers than are ready to buy on the scale from 0 to 10, 0 - not ready, 10 - ready; the bigger the number, the better) and audience (the bigger the audience, the better). I need to maximize customers, ready_to_buy and audience, and minimize the budget. How do I approach building the optimization function for this? Also, do I need to normalize variables before I plug them into the formula? For example, values in budget can range from$5-1000, but the number of customers per day can be 10 on average, etc.