Studying sum combinations

Since I am interested in math, I occasionally have to solve not-so-easy math problems. Right now I am studying sum combinations. How to do it easier?

I don't even know what to advise you, as I have never been interested in such a question myself. But if I am not mistaken, there is a combination sum calculator at the link https://www.calculator.io/combinations-calculator/ Take a look, I think it will help you in solving your question. And you will find other information useful for a mathematician there as well. 

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