Consider the question. Sarah, Mary, and Tuan decided to go to the restaurant for a meal. They decided to split the cost of the meal evenly. If the total price of the meal comes to $67 and they have a coupon for $4, how much does each person need to contribute to the bill?
 If the answer is '21'; explain the reasoning:
After using the coupon, the final price comes to 67 - 4 = 63 dollars. With three people, they each need to pay 63 / 3 = 21 dollars each.