How many ways are there to select 10 balls from unlimited nunber of red white blue and green balls?

in those 10 balls we can have any combination...I am using here multinomial...

X=No. of red balls(0,1...10)

y=No. of green balls(0,1...10)

z=No. of white balls(0,1...10)

we need co-efficient of x^10 in (x^0+x^1+...+x^10)^3

that is (10+3-1)C3=12C3

Arrangement is also considered here