In 2001, there were about 62.5 thousand golden retrievers registered in the United States. In 2002, the number was 56.1 thousand. Which linear equation best represents this information?
a ) y = 6.4x + 2001
b ) y = -6.4x + 12868.9
c ) y = 6.4x - 12743.9
d ) y = -6.4x + 2002