1. fix the position of the S's at the ends, so its 5!x2!, the 2! is for the swap between the S's.
3. (a) to be greater than 400 the first number that has to be chosen can't be 1,2,3 so there are 6 possibilities for the first one and then there is 9-1 then 9-2. mulitply all those together for the...