Need help with another binary operation.

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On the set {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, I define the operation ⊗ to be like our standard multiplication, except that the result is just the last digit of the product. For example, 4 ⊗ 7 = 8, since 4 × 7 = 28, and 8 is the last digit of 28. Noticing that 1 is the identity element for ⊗, find the inverse of each element of the set with respect to ⊗ (or if an element doesn’t have an inverse,