So, now, we know that based on the linear airy’s theory, the dynamic pressure due to a propagating width is given by equation 20. So, the dynamic pressure, we have worked out a few problems also. So, the dynamic pressure is going to change with respect to z and it is going to at each elevation; it is going to be a varying as a sin function or a cosine function. So, now the parameter F of F k x can be obtained from this 2 a, that is the area. And the pressure has to be integrated over height as a column, because you are interested in finding out, the pressure the force acting on this column. So, what is the location at this is equal to minus d, z equal to minus d and at this point it will be d minus h but negative. So, you will have minus d to h minus d.