For a 2 by 2 matrix [[a, b], [c, d]], the inverse is 1/(ad − bc) times [[d, −b], [−c, a]]. The determinant of [[1, 3], [−1, 2]] is 1·2 − 3·(−1) = 5, so its inverse is 1/5 [[2, −3], [1, 1]]. This matches choice C.
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