The pressure can be solved using the following formula:
P = mg / A
Where: P = pressure
mg = mass * gravity = W = 10.5 N
A = l*w
Solving for A (maximum):
A = 8*3
A = 24 sq. cm
Solving for A (minimum):
A = 15*8
A = 120 sq. cm
Substituting into the first equation:
Pmax = 10.5 N / 24 sq.cm
Pmax = 0.4375 Pa
Pmin = 10.5 N / 120 sq.cm
Pmin = 0.0875 Pa