Answer
$ 15760_{nine} $
Work Step by Step
Rightmost column: $4+5=9=1\times 9+0\times 1=10_{nine}$
record the $0$, carry the 1.
$\left[\begin{array}{lllll}
& & & 1 & \\
& 6 & 7 & 8 & 4_{nine}\\
+ & 7 & 8 & 6 & 5_{nine}\\
& - & - & - & -\\
& & & & 0_{nine}
\end{array}\right.$
Next column:
$1+8+6=15=1\times 9+6\times 1=16_{nine}$
record the $6$, carry the 1.
$\left[\begin{array}{lllll}
& & 1 & 1 & \\
& 6 & 7 & 8 & 4_{nine}\\
+ & 7 & 8 & 6 & 5_{nine}\\
& - & - & - & -\\
& & & 6 & 0_{nine}
\end{array}\right.$
Next column:
$1+7+8=16=1\times 9+7\times 1=17_{nine}$
record the $7$, carry the 1.
$\left[\begin{array}{lllll}
& 1 & 1 & 1 & \\
& 6 & 7 & 8 & 4_{nine}\\
+ & 7 & 8 & 6 & 5_{nine}\\
& - & - & - & -\\
& & 7 & 6 & 0_{nine}
\end{array}\right.$
Next column:
$1+6+7=14=1\times 9+5\times 1=15_{nine}$
record the $15$,
Result =$ 15760_{nine} $
