Question 278343
7. 
2X+2Y+4Z=10 --> x + y + 2z = 5
3X+3Y=15 --> x + y = 5
4X+12Y+4Z=44 --> x + 3y + z = 11
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Reducing often helps.
x + y + 2z = 5
x + y + 0z = 5
---------------- Subtract
2z = 0
z = 0
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x + 3y = 11
x + y = 5
----------- Subtract
2y = 6
y = 3 
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x = 2
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Do the others in a similar manner
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Don't type in all those lines.