I need a difference between 2 colums in diffrent sheets [Closed]

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Registration date
Friday February 26, 2016
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Last seen
February 26, 2016
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Hi

example
sheet 1 sheet 2

ndc quantity ndc quantity difference
11111 10 11111 5
22222 20 22222 15
33333 30 33333 25
44444 40 44444 35

I need a formula to calculate difference in quantity with same ndc