\( \mathbf{16} - 8 = 8 \)
\( 18 - \mathbf{9} = 9 \)
\( 16 - \mathbf{9} = 7 \)
\( \mathbf{17} + 9 = 18 \)
\( \mathbf{17} - 9 = 8 \)
\( \mathbf{15} - 7 = 8 \)
\( \mathbf{16} - 7 = 9 \)
\( 18 - \mathbf{8} = 10 \)
\( \mathbf{8} + 9 = 17 \)