Find the length of a surface with a width of 20 mm if a body with a mass of 2 tons exerts a pressure of 21 MPa.

d = 20 mm = 0.02 m.
m = 2 t = 2000 kg.
P = 21 MPa = 21 000 000 Pa.
g = 9.8 m / s ^ 2.
l -?
P = F / S, where F is the force that acts on the area S.
Under the action of gravity, the body has a weight F = m * g.
S = d * l, the area of a rectangular surface S is equal to the product of the width d by the length l.
P = m * g / d * l.
l = m * g / d * P.
l = 2000 kg * 9.8 m / s ^ 2 / 0.02 m * 21 000 000 Pa = 0.047 m.
Answer: the length of the surface is l = 0.047 m.