He bought 60-cent candy bars with "c" dollars.
Then he ate "n" of them.
We have to find how many are left.
We don't know the value of "c" or "n" but we can write the solution in function of them.
We can calculate the number of candy bars as the quotient between the money he spent, c, and the price of the candy bars in dollars ($ 0.60).
We can define the quantity he bought as B:
Then, if he ate n of them, we will be left with X candy bars, being X:
Answer: he has c/0.6 - n candy bars left.