An array of power transistors, dissipating 6 w of power each, are to be cooled by mounting them on a 25cm ×25cm-square aluminum plate and blowing air at 35°c over the plate with a fan at a velocity of 4 m/s. the average temperature of the plate is not to exceed 65°c. assuming the heat transfer from the back side of the plate to be negligible and disregarding radiation, determine the number of transistors that can be placed on this plate.