This is given by the multinomial coefficient:
[tex]\dbinom{11}{1,4,4,2}=\dfrac{11!}{1!4!4!2!}=34650[/tex]
If you're not familiar with the multinomial coefficient, you may be able to see it more clearly if you count the number of possible combinations taking each distinct letter [tex]n[/tex] times, where [tex]n[/tex] is the number of times it shows up in the original word.
[tex]\underbrace{\dbinom{11}1}_{\text{M}}\underbrace{\dbinom{10}4}_{\text{I}}\underbrace{\dbinom64}_{\text{S}}\underbrace{\dbinom22}_{\text{P}}=\dfrac{11!}{1!10!}\dfrac{10!}{4!6!}\dfrac{6!}{4!2!}\dfrac{2!}{2!0!}=\dfrac{11!}{1!4!4!2!}[/tex]
