Since the hut is round we can assume that the floor is a circle, so in order to find the diameter of the floor we need to use the circle's area which is given by:
circle area = π*r²
In this case we have the area of the floor, so we can solve for "r". We have:
12.56 = π*r²
π*r² = 12.56
r² = 12.56/π
r² = 12.56/3.14 = 4
r = sqrt(4) = 2 m
The diameter is 2*r so the diameter of this room is 4 m.
