What is the value of 8²/3?

A fractional exponent $\frac{m}{n}$ means take the $n$th root and then raise to the $m$th power. So $8^{2/3} = \left(\sqrt[3]{8}\right)^2 = 2^2 = 4$, choice D. Taking the root first keeps the numbers small. Choice A (16) is $8 \times 2$ or $4^2$, which comes from treating the exponent as multiplying 8 by 2. Choice B (6) comes from $8 \times \frac{2}{3} \approx 5.3$ rounded, or from subtracting 2 from 8, neither of which is valid. Choice C (2) is the cube root alone, forgetting to square it.