Question 1173603
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Actually,  it is  A  JOKE  PROBLEM,


because the answer is known to every housewife,  based on her common sense,

as I once noticed before,  answering this question couple of days ago  (I am lazy to search for this link . . . ).



There is no need to solve equation/equations in this case - the answer should be  OBVIOUS  based on common sense.


But some people do not distinct a joke from a real problem . . . 



The intention of this problem is simply to check if a recipient has enough common sense to answer momentarily . . .