Puzzle: Find the missing number?

Question

If

4+5+4+5=81
5+6+5+6=16
6+7+6+7=64
1+2+1+?=16

What is the missing number?

Answer 1

Third number is same as first one and fourth is same as second one in all the cases so the missing number is 2.

Answer 2

4+5+4+5=18, 1+8=9, 9*9=81
5+6+5+6=22, 2+2=4, 4*4=16

following the same logic...
missing number is 0

Comments

Answer by the same logic can also be 9. Both 0 and 9 are the correct answers!

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@Atul: Don't think too much its very simple puzzle...