Part A The registration period for the race is under way, and as the word is getting out, the number of participants registering is growing exponentially. The numbers from the first two days of registration are shown in the table. ___Participants on Opening Day of Registration 15
Participants 1 Day after Opening Day of Registration 21
Use the data in the table and the general form of an exponential growth equation, y = a(1 + r)x, to write an equation modeling the exponential growth of registrations, where x is the number of days since registration opened, a is the initial number of registrations, r is the rate of growth of registrations per day, and y is the total number of registrations.