\[\boxed{\mathbf{35.}}\]
\[\textbf{а)}\ 50 - 20 = 30\]
\[53 - 50 = 3\]
\[53 - 3 = 50\]
\[53 - 2 = 51\]
\[60 - 10 = 50\]
\[66 - 60 = 6\]
\[66 - 6 = 60\]
\[66 - 5 = 61\]
\[\textbf{б)}\ 100 - 10 = 90\]
\[100 - 60 = 40\]
\[100 - 1 = 99\]
\[99 - 7 = 92\]
\[70 - 20 - 1 = 50 - 1 = 49\]
\[100 - 30 - 0 = 70\]
\[86 - 4 - 10 = 82 - 10 = 72\]
\[55 - 5 - 50 = 50 - 50 = 0\]