Answer: C. 5.8 inches
Explanation:
The formula for calculating the Surface area of a cube is give as :
surface area = 6

Where a is the length of an edge
That is :
200 = 6

divide through by 6
200/6 =

that is
= 33.33333333
take the square root of both sides
a = 5.773502692
Therefore the length of an edge ≈ 5.8 inches