The vx2 in the equation for average pressure in part c. should more properly be designated as the average of the square of the x-components of the velocities vx2 The N particles inside the container move at different speeds and in different directions. How is vx2 related to the average of the square of the speeds v2. Hint: Assume that one-third of the particles move in each of the three directions (x, y,z), and ask yourself if there is any reason the average would be different in different directions.