Let X be the set of all natural numbers x with the property that x=4a+13b for some natural numbers a and b. For example, 30X since 30=4(1)+13(2), but 5=2X since there's no way to add 4's and 13 's together to reach 5 . (It's not a multiple of 4, and adding 13 goes over.) Use strong induction to prove that nX for all integers n36. Hint: it should be easy to show that k+1X if k3X. You may need multiple base cases for this