\[\boxed{\text{5.4}\text{3}\text{4.}}\]
\[\textbf{а)}\ 7^{2} - 6^{2} = 49 - 36 = 13\ \]
\[\textbf{б)}\ 3^{3} - 17 = 27 - 17 = 10\ \]
\[\textbf{в)}\ 5^{2} \cdot 8 = 25 \cdot 8 = 200\ \]
\[\textbf{г)}\ 64\ :2^{3} = 64\ :8 = 8\ \ \]