The answer would be C. 250N.
Net force is defined as the sum of all forces acting on an object. But you need to take into account, the direction of the forces. All forces going to the right is usually positive, and those on going to the left is negative. Let's take your problem into account:
F1 = 200 N to the right (positive)
F2 = 500N to the left (negative)
F3 = 100 N to the right (positive)
F4 = 50 N to the left (negative)
Fnet = F1 + F2 + F3 + F4
Put in what you know with the proper sign:
Fnet = F1 + F2 + F3 + F4
Fnet = 200N +(-500N) + 100N + (-50N)
Fnet = 200N +(-500N) + 100N + (-50N)
Fnet = (-300N) + 100N + (-50N)
Fnet = (-200N) + (-50N)
Fnet = -250 N
Because the sign of the result is negative, we know that the force is to the left. So your final answer would be:
250N to the left
