The number of non-negative integral solution `x_1 + x_2 + x_3 + x_4 <=n` (where n is a positive integer) is :

Find the number of non negative integral solutions of x_1 + x_2 + x_3 + 4x_4 = 20

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

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

Find the number of non-negative integral solutions of x_1+x_2+x_3+4x_4=20.

Find the number of non-negative integral solutions of x_1+x_2+x_3+4x_4=20.

Find the number of non-negative integral solutions of x_1+x_2+x_3+4x_4=20.

(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