Mass of girl =55kg
acceleration due to gravity =9.8m/s^2
So, the force she is applying on the floor must equal
55× 9.8 N
(Because force =mass ×acceleration)
=539N
Now, according to newton's third law the floor must be applying the same force on the body in the opposite direction.
So the force applied here by the floor is 539N upward.
Option "C" is the correct one.