Standard +0.8 This is a proof by induction requiring students to manipulate algebraic expressions involving powers. While the technique is standard for Further Maths, the factorization step (extracting 8·2^{3k} - 3·3^k from 2^{3(k+1)} - 3^{k+1}) requires careful algebraic manipulation and insight to reveal the factor of 5, making it moderately challenging but within reach of well-prepared FM students.