Amerchant uses the rule f (c) = (2 × c) + 1 to set his selling price.

If merchant uses the rule f (c) = (2 × c) + 1 to set his selling price, we can assume that c is for the total number of items that he was able to sold while f(c) is the function equivalent to the total gain.
If c=1, then f(c)=3 while if c=2, f(c)=5.

The answer of the above question is