Ishaan is 72 years old and William is 4 years old. How many years will it take until Ishaan is only

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Ishaan is 72 years old and William is 4 years old. How many years will it take until Ishaan is only 5 times as old as William?

Express Ishaan and William's age since today where y is the number of years since today, we have:
i = 72+y
w = 4+y

We want the time for Ishaan age will be 5 times William's age:
i = 5w
72 + y = 5(4 + y)

We plug this equation into our search engine and get:
y = 13