The student council at a local high school is selling raffle tickets for $3 each. 
 The amount of money raised is
 a function of the number of tickets sold. 
 
 This function is given by the equation m=3n, where n is the number of tickets sold and m is the amount of money raised. 
 
 Which set below would represent a reasonable domain for this function?
 
 (1) {0, 1, 2, 3, ...}
 (2) {0, 3, 6, 9, ...)
 (3) (1.5, 3, 4.5, 6, 7.5,...}
 (4) {...-2, -1, 0, 1, 2,...}