Question 342378
a.   X + Y = 10 ,  3X + Y = 12
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3x + y = 12
 x + y = 10
----------- Subtract
2x = 2
x = 1
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y = 9
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b.  2X + 5Y = 19 ,  3X + 3Y = 15
3X + 3Y = 15 --> 2x + 2y = 10
2x + 5y = 19
2x + 2y = 10
------------ Subtract, do it like the 1st one.
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c.  4X + Y = 22 ,    2X + 3Y = 16
4x + y = 22 --> y = 22 - 4x
Sub for y in the 2nd eqn
2x + 3(22 - 4x) = 16
Solve for x, then sub into either eqn to find y.
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d.  12X + Y = 174 ,  8X - 2Y = 36
y = 174 - 12x
Proceed as in c.