Answer:
10 years.
Step-by-step explanation:
Present age of Mr. Tanaka = 35 years
Present age of his son = 5 years
Now let the number of years be x. As after x years both of their age will increased by x years, therefore
After x years age of Mr. Tanaka = 35 + x
After x years age of his son = 5 + x
According to question,
Mr.Tanaka's age after x years = 3 (His son's age after x years)
35 + x = 3 (5 + x)
Further solving,
35 + x = 15 + 3x
3x - x = 35 - 15
2x = 20
x = 10
Therefore after 10 years Mr. Tanaka's age will be exactly three times as old as his son. As after 10 years Mr. tanaka's age will be 45 and his son's age will be 15.
