Permutation and Combination

Question

How many solutions are there to the equation :

X1 + X2 + .... + X5 = 21

0 <= X1 <= 3 , 1 <= X2 < 4 , and X3 >= 15 ?

Please solve it without using Generating function

Comments

u have asked to solve without using mgf????

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Yeah i know that's the solution  for @Magma , she asked for solving it using generating function. I want to learn using inclusion exclusion, i know using generating function

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Na462  thank you