You seem to want to calculate the pressure exerted by the plate on the earth's surface (specific and the dimensions should have been stated clearly in the drawing).
Pressure exerted = Force/Area
In this case Force is equal to the weight of the plate.
Weight of plate = mass*g ( acceleration due to gravity)
Dimensions of plate are length = 3500 mm = 3.5m
Width = 2300 mm = 2.3 m
Thickness = 75 mm = 0.075 m
Assuming the material of construction of plate to be steel ( it has not been stated in the question) , density of steel(assumed) = 7750 Kg/m^3
Volume of plate = 3.5*2.3*0.075 m^3 = 0.60375 m^3
Therefore Weight of one plate = 7750*0.60375*9.8 =45854.8125
Force exerted by plate on the earth = Weight/Area
= 5696.25 Pascal
= 5.7 KPa
Assumptions : Material of construction of plate as steel with density(7750 Kg/m^3) , single plate lying flat on the earth surface.