Answer:
Explanation:
Assume there exists integer k such that 3k=a+1.
4+7a
=7a+4
=7(a+1)-3
=7(3k)-3
=3(7k-1)
This implies that if there exists integer k such that 3k=a+1 then there is integer 7k-1 such that 3(7k-1)=4+7a
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