Matt is 3 times as old as Jan In 7 years he will be twice as old as she will be then. How old are they now

m=3j

m+7=2(j+7) two equations in two unknowns.solve by substitution of 3j for m in the second equation.

3j+7=2j+14

-2j=-2j

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j+7=14

-7=-7

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j=7