The number of coffee shops in a certain country can be modeled by the quadratic function ​f(x)105x²+680x+4296, where​ f(x) is the number of coffee shops and x is the number of years after 2000. Complete parts a and b.
a. Find the number of coffee shops in 2006.
b. If the trend described by the model​ continues, predict the year after 2000 in which the number of coffee shops will be 21;500.