The estimated demand function for pizza is Qd = 500 - 20P, where P is the price of pizza and Qd is quantity of pizza demanded. If the price of pizza is $12, the predicted quantity of pizza demanded is ____________. If the actual quantity of pizza demanded is 280, the residual is ____________.
a) 260; 500
b) 260; 20
c) 476; 9
d) 500; 20