P
D=AR
Pm MR
Pc
Pl MC=AC
Q
Qm Qc Ql
Larry will choose (Pl,Ql) to sell as many drinks as possible without losing money. At this point, Pl=AR = MC=AC, so the profit is zero and MR is negative, but Q1 is the largest quantity it can reach.
Curly will choose (Pc,Qc) to bring in as much revenue as possible. At this point, MR=0 which means with one more unit of product, the Marginal Revenue will be negative, and bring down its total revenue.
Moe will choose (Pm,Qm) to make the largest possible profits. At this point, MR=MC. This means with one more unit of product, the Marginal Revenue will be less than its Marginal Cost, and make negative profit to the saloon.