7|(3^(8)×5^(7)+3^(6)×5^(8)
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Răspuns :

3^8×5^7+3^6×5^8=
=3^6
×5^7×(3^2+5)=
=3^6×5^7×(9+5)=
=3^6×5^7×14=
=3^6×5^7×2×7    deci divizibil cu 7