1) Firstly, we are working with real numbers, so we need to garantee that:
\(x \geq 0 \\ \sqrt{x} \geq \sqrt{0} \\ \sqrt{x} \geq 0\)
2) Secondly, we need to look at the inequation:
\(\sqrt{x} \leq 8 \\ ( \sqrt{x} )^2 \leq 8^2 \\ x \leq 64\)
3) Then, the solution is given by:
\(\boxed {0 \leq x \leq 64}\)
Letter D
