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The number of sandwiches the band sold: 73

The cost to make one sandwich: S

The profit the band earns from one sandwich: 0.2S

The amount of money that the band receives for selling one sandwich: S+0.2S

Although the band gets S+0.2S dollars for each sandwich sold, the S portion only makes up for the dollars they spent making the sandwich. The profit, or the actual amount of money they gain from selling the sandwich, is that extra 20% of the original price, or 0.2S.