Let 'x' be Karen's age
'y' be Lori's age
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x = 2y ----equation 1
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-three years from now
(x+3) + (y+3) = 42 ---equation 2
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Substitute equation 1 to equation 2
(2y+3) + (y+3) = 42
2y + 3 + y + 3 = 42
2y + y = 42 - 3 - 3
3y = 36
y = 12
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Substitute y=12 to equation 1
x = 2y
x = 2(12)
x = 24
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Therefore Karen is 24yrs old