Question 355179
you must mean, how old will you be when you are 3 times your daughters age, not the other way around
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your age=30, your daughter =5
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let x=additional years 
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30+x=3*(5+x)
30+x=15+3x
30-15=3x-x
15=2x
7.5=x
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in 7.5 years you will be 3 times your daughter's age
validate
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30+x=3*(5+x)
30+7.5=3*(5+7.5)
37.5=3*12.5=37.5