Chapter 12 - Sequences; Induction; the Binomial Theorem - 12.1 Sequences - 12.1 Assess Your Understanding - Page 807: 65

$\sum_{k=1}^{n}(\frac{3^k}{k})$

We can see that this is the sum of the $6$ fractions in which the first denominator is $3$, and gets multiplied by $3$ in each term and in which the numerator of the nth term is $n$. Hence the summation formula is: $\sum_{k=1}^{n}(\frac{3^k}{k})$