there is an error in your problem - I have figured it out based on the choices given.
Your problem should read:
2 ^ (4/3)
(It could be misread as 2^(4) divided by 3. But no answer fits that solution.
So - we will go with: 2 ^ (4/3)
First convert 4/3 to 1.3333 (we will use 4 places for the best answer)
2^1.3333 gives us 2.5198
NOW look at the choices.
The cube root of 8 is an even 2. That's not it.
The square root of 8 is 2.8284. No.
The cube root of 16 is 2.5198 BINGO - that's the one.
The square root of 16 is 4. No.