Her average in first three test = 89
This means, her total scores in first three test were = 3 x 89 = 267
Her average in four tests = 91
This means, her total scores in four tests are = 364
267 give the sum of first three test scores. and 364 give the sum of scores with fourth test adding in three tests.
So, subtracting 267 from 364 will give us the scores of Fourth test.
Scores of Fourth test = 364 - 267 = 97
Thus, Samantha's Claim is correct
