Any of 28 of the Level-3 employees for position A. Any of 18 of the Level-2 employees for position B. Any of 18-1 = 17 of the remaining of the Level-2 employees for position C. Any of 7 of the Level-3 employees for position D. In all, it gives 28*18*17*7 = 59976 different ways to fill the positions.