Example 6. Father's age is 48 years old, son's age is 20 years old. How many years later will the father's age be 3 times the son's age?
Solution: Let $\mathrm{x}$ years later, the father's age is 3 times the son's age.
We have $48+x=3(20+x)$. Solving for $\mathrm{x}$, we get $\mathrm{x}=-6$.
This means that 6 years ago, the father's age was 3 times the son's age. Conventionally, there is no such expression as “-6 years later.” However, according to the meaning of negative numbers, we can interpret “-6 years later” as 6 years ago. Therefore, this conclusion is correct, and the answer should be written as:

Answer: 6 years ago, the father's age was 3 times the son's age.