Artificial intelligent assistant

How many kg we need to take a mixture of $50$ kg and value of $720$ euro? how many kilos of coffee value of $900$ euro per kg , and how many of the $600$ euro must mix , to obtain a mixture of $50$ kg and value of $720$ euro per 720 per kg? Could anyone give any hints?

Solve the following system of two equations in two variables:

* $x+y=50$
* $(900x+600y)/50=720$

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