Answer
4
Work Step by Step
We are asked to evaluate $\sqrt 64-\sqrt[3] 64$.
We know that $\sqrt 64=8$, because $8^{2}=8\times8=64$
And we know that $\sqrt[3] 64=4$, because $4^{3}=4\times4\times4=64$
Therefore, $\sqrt 64-\sqrt[3] 64=8-4=4$