Final answer:
The number of Golden Arch restaurants reached 5,000 in the year 1978.
Step-by-step explanation:
To find the year when the number of restaurants reached 5,000, we need to analyze the given information. In 1955, the first restaurant opened, and by 1958, it sold 100 million hamburgers. By 1959, there were 100 Golden Arch restaurants, and in 1963, there were 500. We know that fifteen years later, the 5000th restaurant opened. So, we need to determine the year that is fifteen years after 1963.