You can put this solution on YOUR website! x = child's current age
x + 12 = age in 12 years
3x - 6 = "six years less than triple her current age"
x+12 = 3x-6
x+12 + 6 -x = 3x-6 +6-x (added 6-x to each side)
18 = 2x
18/2 = 2x/2
9 = x
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Ans: the child is years old
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Check: in 12 years, the child will be 21
and 3 * 9 - 6 = 27-6 = 21 (ok)