Corey,
 When you are walking up you go a distance of 1 floor in 75 seconds so your speed is 1/75 (one floor every 75 seconds).
 When you are riding up, your speed is 1/45.
 When you are walking up an operating escalator, your speed is combined: 1/45 + 1/75.
 Remember that time = distance/speed. The distance is still 1 floor. So t = 1 / (1/45 + 1/75). Calculate t.
Cheers,
Stephen La Rocque.
