Answer
$13_{seven}$
Work Step by Step
Start with the right-most column.
$2$ is less than $6$.
Borrow 1 $seven$ from the $3$ in the next column.
In base ten: ($2+7$)-$6$=$3$
Record: $3_{seven}$
$\left. \begin{array}{llll}
& 3 & 2_{seven}\\
- & 1 & 6_{seven}\\
-- & -- & --\\
& & 3_{seven}
\end{array}\right.$
Next column:
$(3-1)=2$ (we borrowed one seven)
$2-1=1$
record the 1:
Result: $13_{seven}$