\[\boxed{\mathbf{16.}}\]
\[\textbf{а)}\ 40 - 31 = 9\]
\[70 - 4 = 66\]
\[50 - 18 = 32\]
\[60 - 22 = 38\]
\[80 - 6 = 74\]
\[90 - 43 = 47\]
\[\textbf{б)}\ 70 - 7 - 33 = 63 - 33 = 30\]
\[80 - 19 - 51 = 61 - 51 = 10\]
\[100 - 40 - 17 = 60 - 17 = 43\]
\[37 + 43 - 8 = 80 - 8 = 72\]
\[90 - 68 + 8 = 22 + 8 = 30\]
\[14 + 86 - 1 = 100 - 1 = 99\]