A ticket selling company is keeping track of how many tickets they have remaining for a concert as a function of the number of minutes since they began selling them. The data is shown in the table below. Number of minutes, x - 5 10 15 20 25 30
Tickets remaining, y - 6822 6180 5722 5008 4195 3890

(a) Find a linear regression equation, in the form y = ax + b, that best fits this data set. Round each parameter to the nearest whole number.

(b) According to this model, would tickets still be on sale after an hour and a half? Justify your answer.