Thinking Mathematically (6th Edition)

$13_{seven}$
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: $13_{seven}$