\[\boxed{\mathbf{3.}\mathbf{162}}\]
\[\textbf{а)}\ 100 - 4 = 96\ :16 = 6 \cdot 12 =\]
\[= 72 + 28 = 100\]
\[\textbf{б)}\ 75 - 29 = 46\ :23 = 2 \cdot 18 =\]
\[= 36\ :36 = 1\]
\[\textbf{в)}\ 90 - 6 = 84\ :14 = 6 + 19 =\]
\[= 25 \cdot 3 = 75\]
\[\textbf{г)}\ 92 - 47 = 45\ :15 = 3 + 23 =\]
\[= 26\ :13 = 2\]
\[\textbf{д)}\ 100 - 16 = 84\ :12 = 7 + 9 =\]
\[= 16 \cdot 3 = 48\]