x+4/7+y = 4/7
=> (x + 4)7 = 4(y + 7)
=> 7x + 28 = 28 + 4y
=> 7x = 4y
=> x/4 = y/7
=> x + y/4 + 7 = x/4 = y/7 mà x + y = 77
=> 77/11 = x/4 = y/7
=> 7 = x/4 = y/7
=> x = 28; y = 49
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