\[\left( 64^{\frac{1}{4}} - 36^{\frac{1}{4}} \right)\left( 64^{\frac{1}{4}} + 36^{\frac{1}{4}} \right) =\]
\[= \left( 64^{\frac{1}{4}} \right)^{2} - \left( 36^{\frac{1}{4}} \right)^{2} =\]
\[= \left( 8^{2} \right)^{\frac{1}{2}} - \left( 6^{2} \right)^{\frac{1}{2}} = 8 - 6 = 2\]