An apartment building has 7 floors and there are 20 steps between each floor. Mickey lives on 5th floor. Mickey must climb steps to get home.
Mickey has to go from the 1st floor to the 5th floor, so he climbs 5 - 1 = 4 staircases to go home. There are 20 steps on each staircase, so he has to climb 20*4 = 80 steps in total.