1/4X - Y = - 5
1/2X - 1/7Y = 3
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1/2X = 1/7Y + 3
1/4X = 1/14Y + 3/2
1/4X = Y - 5
--------------------
1/14Y + 3/2 = Y - 5
( Y + 21 ) / 14 = ( 14Y - 70 ) / 14
Y + 21 = 14Y - 70
13Y = 91
Y = 7
-----------------------
1/4X = 7 - 5
1/4X = 2
X = 8
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ОТВЕТ ( 8 ; 7 )