1. (6) Let P(n) be the statement that a postage of n cents can be formed using a combination of 4-cent stamps and 7-cent stamps. The parts of this exercise outline a strong induction proof that P(n) is true for n 2 18. ts P(18), P(19), P(20), and P(21) are true, completing the basis step of the proof. (b) What is the inductive hypothesis of the proof