请教standard deveation＆mean的关系，prep题

For a certain examination, a score of 58 was 2 standard deviations below the mean, and a score of 98 was 3 standard deviations above the mean.  What was the mean score for the examination?

(A) 74

(B) 76

(C) 78

(D) 80

(E) 82

58+2X=98-3X

X=8

mean=74