Physics: Pressure and Mass

Four acrobats of mass 61.5 kg, 68.0 kg, 62.0 kg, and 55.0 kg form a human tower, with each acrobat standing on the shoulders of another acrobat. The 61.5-kg acrobat is at the bottom of the tower.

(a) What is the normal force acting on the 61.5-kg acrobat? (Enter the magnitude only.) 

(b) If the area of each of the 61.5-kg acrobat’s shoes is 510 cm2, what average pressure (not including atmospheric pressure) does the column of acrobats exert on the floor?  (c) Will the pressure be the same if a different acrobat is on the bottom?