Answer
$366_{seven}$
Work Step by Step
Start with rightmost column.
$3$ is less than $3$.
Borrow 1 $seven$ from the $1$ in the next column.
In base ten: $(7+3)-4=6$
Record: $6_{seven}$
$\begin{array}{llll}
& 5 & 6 & 3_{seven}\\
- & 1 & 6 & 4_{seven}\\
-- & -- & -- & --\\
& & & 6_{seven}
\end{array}$
Next column:
$(6-1)=5$ (we borrowed one eight)
$5$ is less than $6$... borrow 1 $seven$ from the $5$
$(5+7)-6=6$
Record the $6$.
$\begin{array}{llll}
& 5 & 6 & 3_{seven}\\
- & 1 & 6 & 4_{seven}\\
-- & -- & -- & --\\
& & 6 & 6_{seven}
\end{array}$
Next column:
$5-1=4$ (one was borrowed)
$4-1=3$
Record the $3$.
Result: $366_{seven}$
