\[\boxed{\mathbf{5.}}\]
\[30 - 3 = 27\]
\[30 - 7 = 23\]
\[30 - 9 = 21\]
\[50 - 4 = 46\]
\[50 - 7 = 43\]
\[50 - 8 = 42\]
\[60 - 2 = 58\]
\[60 - 6 = 54\]
\[60 - 9 = 51\]
\[80 - 3 = 77\]
\[80 - 4 = 76\]
\[80 - 6 = 74\]