Gimme Shelter Roofers maintains a file of past customers, including a customer number, name, address, date of job, and price of job. It also maintains a file of estimates given for jobs not yet performed; this file contains a customer number, name, address, proposed date of job, and proposed price. Each file is in customer number order. Design the logic that merges the two files to produce one combined file of all customers, whether past or proposed, with no duplicates; when a customer who has been given an estimate is also a past customer, use the proposed data.