d = diameter of the seat = 12 inch
we know that , 1 inch = 0.0254 m
hence
d = diameter of the seat = 12 inch = 12 (0.0254) m = 0.305 m
r = radius of seat = diameter/2 = d/2 = 0.305/2 = 0.1525 m
A = area of seat = πr²
m = mass of the person = 65 kg
g = acceleration due to gravity = 9.8 m/s²
F = force due to weight of person on the seat = mg
pressure on the seat is given as
P = F/A
P = mg/A
P = mg/(πr² )
inserting the values
P = (65 x 9.8)/((3.14) (0.1525)²)
P = 8723.1 N/m²