To find the possible additional amounts Bob will spend, we need to consider that he has already spent $18 and the total amount he can spend is at most $31. Let's denote the additional amount he will spend as "c" (in dollars).
We can express the inequality as follows:
c ≤ $31 - $18
Simplifying the right side:
c ≤ $13
Therefore, the possible additional amounts Bob will spend, represented by "c," are less than or equal to $13. The inequality is c ≤ $13.