Pressure is force divided by area, P = F/A, so we don't actually care about the dimension of depths, the 0.20 m, in this problem at all. All we have to do to get the area of the boxes is multiple the length times the width, or A= Area = 0.60*0.50 = 0.30 m², then we can just take the 70 N of force and divide by that area to get pressure. So P = 70 N/0.30 m² = 233.33 Pa. Pascals (Pa) are the standard unit of pressure and are the same thing as N/m².