With what force does the air press on the 10 cm square lid at atmospheric pressure?

P = 101325 Pa.
a = 10 cm = 0.1 m.
F -?
By definition, the pressure P is the ratio of the force F to the area S on which this force acts.
P = F / S.
F = P * S.
Since the chair cover is square, S = a ^ 2.
F = P * a ^ 2.
F = 101325 Pa * (0.1 m) ^ 2 = 1013.25 N.
Answer: a force F = 1013.25 N acts on the chair cover