Standard +0.3 This is a standard proof by induction with divisibility, a core FP1 topic. The algebraic manipulation in the inductive step (factoring out 7 from 2·2^{n+1} + 5·9·9^n - 7·5·9^n) is straightforward once students recognize the standard technique. While it requires careful algebraic handling, it's a routine application of the induction framework with no novel insight needed, making it slightly easier than average.