Question 989232
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x=per minute charge; b=flat monthly fee; y=total monthly charge
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mx+b=y
280x+b=$165
570x+b=$310 Subtract second equation from first.
-290x=-$145
x=$0.50
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$0.50(280)+b=$165
$140+b=$165
b=$25
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ANSWER: y=$0.50x+$25
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CHECK
$0.50(570)+$25=$310
$285+$25=$310
$310=$310