How many strings can be formed by reordering the letters ABCDEF so that each string contains the substring EA or the substring CE or both?
So I thought considering EA as single character there are 5! ways Considering CE as a single character there are $5!$ ways considering CEA as a single character there are $4!$ ways which is counted in both EA or CE case so is the total $5!+5!-4!=216$?