Final answer:
The upward force of the floor upon the block, while the custodian is pushing downward with 161.0 N, is 602.0 N.
Step-by-step explanation:
When a 45.0-kg block is at rest on the floor and a custodian applies a downward force of 161.0 N, the floor must exert an equal and opposite force to not only support the weight of the block but also to counter the additional downward force. The weight of the block is the force due to gravity, which is calculated by multiplying the mass of the block by the acceleration due to gravity (9.8 m/s2).
For a 45.0-kg block, this weight is 45.0 kg × 9.8 m/s2 = 441.0 N. The total upward force from the floor must balance both the weight of the block and the custodian's force,
so it would be 441.0 N + 161.0 N = 602.0 N.
Therefore, the upward force of the floor upon the block is 602.0 N.