robinetul a curge cu x litri de apa in 1 min
robinetul b curge cu y litri de apa in 1 min=>
x*5 +y*3=190 /*2 => 10*x +6*y=380
x*7+ y*2=200 /*3 => 21*x+6*y=600
================================= (scadem din a doua, prima)
(21*x+6*y) -(10*x +6*y=) = 600-380 <=>
<=> 11*x =220 <=>x=20 =>
=>x*5 +y*3=190 <=> 20*5 +y*3=190 <=> y*3=90 <=>y=30