\[\boxed{\text{6.9.}}\]
\[\textbf{а)}\ 8^{2}\ :4 = 64\ :4 = 16;\ \]
\[16 + 56 = 72;\ \]
\[72\ :18 = 4;\ \]
\[4 \cdot 25 = 100;\ \]
\[100 - 61 = 39.\ \]
\[\textbf{б)}\ 3^{3} \cdot 2 = 27 \cdot 2 = 54;\ \]
\[54\ :6 = 9;\ \]
\[9 \cdot 7 = 63;\ \]
\[63 + 7 = 70;\ \]
\[70 + 230 = 300.\ \]
\[\textbf{в)}\ 10^{2} \cdot 3 = 100 \cdot 3 = 300;\ \]
\[300\ :150 = 2;\ \]
\[2 \cdot 48 = 96;\ \]
\[96 + 44 = 140;\ \]
\[140\ :7 = 20.\ \]
\[\textbf{г)}\ 4^{3}\ :8 = 64\ :8 = 8;\ \]
\[8 \cdot 9 = 72;\ \]
\[72 + 19 = 91;\ \]
\[91\ :13 = 7;\ \]
\[7 \cdot 120 = 840.\ \]
\[\textbf{д)}\ 5^{2} \cdot 8 = 25 \cdot 8 = 200;\ \]
\[200\ :40 = 5;\ \]
\[5 \cdot 60 = 300;\ \]
\[300 - 120 = 180;\ \]
\[180\ :30 = 6.\ \ \ \]