The general rule for add or subtracting fractions is that the fractions must have a common denominator, meaning that the value under the fraction bar must be the same. This rule is also applicable for algebraic fractions.
Therefore, when the question asks "Which of the following can be added without altering any of the fractions?", one should be looking for two fractions with a common denominator. Thus the answer would be the first option, which is the following;
Letting w be the number of wolves on January 1, we know that there are 23 fewer the next year which is given by w-23. We also know that this is a total of 84, so w-23=84.