Machine design

The pinion of a pair of helical gears mounted on parallel shafts is to transmit 4 kW at 8000 rpm. Both gears have 30 degrees helix angle, 20 degrees normal pressure angle and are made of SAE 1040 HR steel with face width of 12 mm. If the pinion has 25 teeth and gear has 100 theeth, what are the minimum gear diameters and what is the required hardness for pinion as BHN, if it needs heat treatment for surface hardness. Take Quality level 7 and safety factor 1.5. Consider strength for size calculations and wear for BHN determination.