Kids today.
3(n + 1) = 3n + 3 when you expand the bracket, since the bracket just indicates that you multiply
everything in it by three.
What zero discussion anyway...? 0 is certainly a number, and qualifies as an integer. In this case, since the seat numbers only go up to 24, the permissible values are that 0 is less than or equal to n, which in turn is less than or equal to seven.