how many PI & EPI does this function have?

[pouri_sb]

hi every one
this is one of our homework. the question is how many Prime Implicants(PI) & Essential Prime Implicants f(a,b,c,d) has?

f(a,b,c,d)= m(0,1,9,11) + don't care(5,6,7,10,15)
tnQ

[pers]

I think , 10 PI and 1 EPI.