\[\boxed{\mathbf{9.}}\]
\[\textbf{а)}\ 30 - 6 = 24\]
\[60 + 3 = 63\]
\[100 - 1 = 99\]
\[70 - 2 = 68\]
\[50 + 4 = 54\]
\[80 - 8 = 72\]
\[\textbf{б)}\ 60 - 7 + 23 = 53 + 23 = 76\]
\[54 + 6 - 2 = 60 - 2 = 58\]
\[100 - 30 - 9 = 70 - 9 = 61\]
\[50 - (11 - 8) = 50 - 3 = 47\]
\[80 - (13 - 6) = 80 - 7 = 73\]
\[90 - (15 - 9) = 90 - 6 = 84\]