Question 120732
1) 
First Equation:  2a=8
Second Equation: a+b=2 
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From the First equation a=4
Substitute into the 2nd equation and solve for "b":
4+b=2
b = -2
Final Solution: a=4 and b = -2
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2) First Equation: 2x+3y=31 
 Second Equation: y=x+7
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Substitute y = x+7 into the 1st equation to solve for x:
2x + 3(x+7) = 31
2x + 3x+21 = 31
5x = 10
x = 2
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Substitute x=2 into y = x+7 to solve for y:
y = 2+7 = 9
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Final Answer: x = 2 ; y = 9
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Cheers,
Stan H.