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=x^20(1+x+x^2+....)^4

=x^20 ( 1/(1-x)^4)

= x^20 (1-x)^-4

So equation is (n+k-1)Cn

We need x^30 ...we have x^20 ..

So n=30-20=10

     k =4

So ans = (10+4-1 )C 10 = 286
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