Question 880709
"When Katy was 12, her father was three times her age"


So her dad was 12*3 = 36 years old when she was 12.


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Katy = 12 yrs old
Dad = 36 yrs old


Add on x years


Katy = (12+x) yrs old
Dad = (36+x) yrs old


We want to know when he'll be twice her age, so


(Dad's Age) = 2*(Katy's Age)


36+x = 2*(12+x)


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Now solve for x



36+x = 2*(12+x)



36+x = 24 + 2x



36 = 24 + 2x-x



36-24 = 2x-x



12 = x



x = 12



In 12 years, Katy will be 12+12 = <font color="red">24 years old</font> and her dad will be 36+12 = 48 years old (notice how he's twice as old, since 48 = 24*2)