The number of U.S. patent applications was 520 thousand in 2010, and it increased by about 21.7

Question:

The number of U.S. patent applications was 520 thousand in 2010, and it increased by about 21.7 thousand per year until 2014. Let n be the number of patent applications (in thousands) during the year that is t years since 2010.
a. Find an equation of a model.
b. Estimate the number of patent applications in 2014.
c. Estimate in which year there were 580 thousand patent applications.