When Clara totaled her scores she inadvertently reversed the units digit and the tens digit of one score. By which of the following might her incorrect sum have differed from the correct one?

When Clara reversed the units digit and tens digit of one score, the difference between the incorrect and correct sum would be determined by the value of the digits switched. If the original score was (10a + b) (where (a) is the tens digit and (b) is the units digit), the incorrect score would be (10b + a). The difference between these two scores is ( (10b + a) - (10a + b) = 9(b - a) ). Therefore, her incorrect sum might have differed from the correct one by a multiple of 9, specifically (9(b - a)), which could be any integer value that is a multiple of 9.