\[\boxed{\mathbf{74.}}\]
\[A = \left\{ 2;4\ 6 \right\}.\]
\[\textbf{а)}\ B = \left\{ 3;6 \right\};\]
\[A \cap B = \left\{ 6 \right\}\text{.\ }\]
\[\textbf{б)}\ \ B = \left\{ 4 \right\};\]
\[A \cap B = \left\{ 4 \right\}.\]
\[\textbf{в)}\ \ B = \left\{ 5;6 \right\};\]
\[A \cap B = \left\{ 6 \right\}.\]
\[\textbf{г)}\ \ B = \left\{ 1;2 \right\};\]
\[A \cap B = \left\{ 2 \right\}.\]