\[\boxed{\mathbf{В.\ 5}}\]
\[\textbf{а)}\ 5;\ \ 16;\ \ 108;\]
\[\textbf{б)} - 18;\ \ 0;\ \ 1;\ \ 115;\]
\[\textbf{в)}\ 4,2;\ \ \frac{2}{3};\ 0,8;\]
\[\textbf{г)} - 1,5;\ - 27,89;\ - 16\frac{3}{7};\]
\[\textbf{д)}\ \frac{2}{5};\ \ 0,4;\ - 3\frac{18}{23};\]
\[\textbf{е)}\ \frac{1}{3}\ и\ 3;\]
\[\textbf{ж)}\ - 15\ и\ 15;\]
\[\textbf{з)}\ \ 2 \cdot 0 = 0\]
\[0,5 \cdot 2 = 1\]
\[\textbf{и)} - 2 + 2 = 0\]
\[3 + ( - 2) = 1\]