Answer: the maximum number of guests that he can invite would be 9
Explanation:
Darnel's retirement party cost $33, plus an additional $1 for each guest he invites. Assuming Darnel wants to invite x guests to his retirement party, the total amount of money that Darnel would spend is
33 + x
if darnel can afford to spend a total of $42 on his retirement party, then
42 = 33 + x
x = 42 - 33 = 9