What is the support force on the floor if someone who weighs 400 N gives someone who weighs 200 N a piggy Back ride?

When a person weighing 400 N gives a piggyback ride to someone who weighs 200 N, the total weight supported by the floor is the sum of both weights. Therefore, the support force on the floor would be 400 N + 200 N = 600 N. This total force is what the floor must counteract to keep the system in equilibrium.