Magazine sales: The following table shows the income from sales of a certain magazine, measured in thousands of dollars, at the start of the given year. Over an initial period the sales grew at a...

Magazine sales: The following table shows the income from sales of a certain magazine, measured in thousands of dollars, at the start of the given year.

Over an initial period the sales grew at a constant rate, and over the rest of the time the sales grew at a constant percentage rate. Calculate differences and ratios to determine what these time periods are, and find the growth rate or percentage growth rate, as appropriate.