In what bases, b, does (b+7) divide into (9b+7) without any remainder.

(9b + 7) / (b + 7) in base 12 =A6 / 16 = 7 with no remainder.

 

(9b + 7) =12^1*9 + 7 = 126 in base 10

(b + 7) = 11 + 7 = 18 in base 10

126 / 18 = 7 with no remainder.