Pressure is the ratio of force and area. Meaning, pressure is the force per area. Therefore, we have
Pressure = Force / Area
We know the sub's window is a circular window. A circle has area A= Pi* r^2. So we have
Pressure = Force / ( Pi * r^2 )
We know the window can withstand 30,000N of force, this gives us
Pressure = 30000 / (Pi * 0.5^2) = 38,197.2
The units are the units of force, N, divided by the units of area, m^2. So our answer has units of N/m^2 or Pascals. Rounding appropriately, our answer is 38,200 Pa or 38.2 kPa. This is about the pressure required from a long-duration blast needed to cause most buildings to collapse.