Show that the postage of six cents or more can be achieved by using only 2-cent and 7-cent stamps by using strong induction.
I know the important step to keep in mind is: Induction step: If $P(m), P(m+1), P(m+2) \ldots P(k)$ is true then $P(k+1)$ is true as well for some $k > m$.
$P(6)$ is true because $6= 2+2+2$
$P(7)$ is true because $7= 7$
$P(8)$ is true because $8= 2+2+2+2$
$P(9)$ is true because $9= 2+7$
Hypothesis: $P(k-3), P(k-2), P(k-1)$, and $P(k)$ is true. We can form a postage of $k+1$ using postage for 2 cents and 7 cents.
I am really unsure what is next. Am I even right with the above steps