1) Y - 15 = 12 - 8Y
Y + 8Y = 12 + 15
9Y = 27
Y = 3
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2) 1 - 7,5 - 5X = 6 - 7,5X
- 5X + 7,5X = 6 + 6,5
2,5X = 12,5
X = 5
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3) 4 - 2X = - 6 - 4X
- 2X + 4X = - 6 - 4
2X = - 10
X = - 5