The scatterplot above shows the number of visitors to a railroad museum in Pennsylvania each year from 1968 to 1980, where represents the number of years since 1968 and represents the number of visitors. The x-axis shows the years since 1968, and the y-axis shows the number of annual visitors. A line of best fit is also shown. Based on the scatterplot and the line of best fit, what is the approximate average annual increase in the number of visitors to the museum?
1,000
2,500
4,700
16,000
