Both the numbers have their last digit 3^x and 3^y so the units digit will be decided by the power of x+y i.e. 3^(x+y)

3^0 = 1

3^1 = 3

3^2 = 9

3^3 = 27

3^4 = 81

here we can see, a pattern with a cycle of 4

Statement 1) x+y = 7, as per the above discussion we can see this is SUFFICIENT

Statement 2) x = 4, we dont know the value of y, hence this is INSUFFICIENT.

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