well i put it into my calculator and i got 16/25 as an answer which is 0.64 as a decimal see comment below...

[latex]( \frac{64}{125} ) ^{ \frac{2}{3} } = \sqrt[3]{(\frac{64}{125}) ^{2} } = \sqrt[3]{ \frac{4096}{15625}} = \frac{16}{25} [/latex]