Answer:
Step-by-step explanation:
Without friction, the firefighter would accelerate downward at 9.81 m/s²
As he/she only accelerates at 2.80 m/s², this means the friction is causing an upward acceleration of 9.81 - 2.80 = 7.01 m/s²
Ff = ma
Ff = 72(7.01) = 504.72 = 505 N upward