Rate in general is a measure of the speed of change of a quantity. We need to calculate by how much the GDP changed. Taking the difference,
$14,291.5 billion-$14,028.7 billion=$262.8 billion
Then, we see that his change happened over 1 year. Hence, the rate of change (rate of growth since it increases) of GDP is $262.8 billion/1 year=$262.8 billion/year.