When a new charter school opened in 2001, there were 490 students enrolled. Write a formula for the equation N , representing the number of students attending this charter school t years after 2001, assuming that the student population: Increased by 20 students per year N = Decreased by 40 students per year N = Increased by 36 students every 2 years N = Decreased by 24 students every 4 years N = Remained constant (did not change) N = Increased by 10 students every semester (twice each year) N =