Write a system of equations to describe the situation below, solve using any method, and fill in the blanks. Zach and his good buddy Chad are both mechanics at a shop that does oil changes. They are in a friendly competition to see who can complete the most oil changes in one day. Zach has already finished 2 oil changes today, and can complete more at a rate of 2 oil changes per hour. Chad just came on shift, and can finish 4 oil changes every hour. Sometime during the day, the friends will be tied, with the same number of oil changes completed. How long will that take? How many oil changes will Zach and Chad each have done?