The number of non-negative integral solutions of `x_1+x_2+x_3+4x_4=20` is

(a) Find the non-negative integral solutions of the equation x+y+z+t=15 , (b) Find the number of non-negative integral solutions x_(1)+x_(2)+x_(3)+4x_(4)=20

The number of non negative integral solutions of 3x+y+z=24 is

The total number of non-negative integral solutions of x_(1)+x_(2)+x_(3)+x_(4)=100 , is

The number of non-negative integral solution x_(1)+x_(2)+x_(3)+x_(4)<=n (where n is a positive integer) is:

The number non-negative integral solutions of x_(1)+x_(2)+x_(3)+x_(4) le n (where n is a positive integer) is: