13. (3 points) Grandpa, Dad, and Xiao Ming's ages are 60 years, 35 years, and 11 years, respectively. In \qquad years, Grandpa's age will be equal to the sum of Xiao Ming's and Dad's ages.
13. (3 points) Grandpa, Dad, and Xiao Ming's ages are 60 years, 35 years, and 11 years, respectively. Then, after 14 years, Grandpa's age will be equal to the sum of Xiao Ming's and Dad's ages.
【Analysis】Let $x$ be the number of years after which Grandpa's age will be equal to the sum of Xiao Ming's and Dad's ages. After $x$ years, the ages of Grandpa, Dad, and Xiao Ming will be: $60+x, 35+x, 11+x$, respectively. According to the condition that "Grandpa's age will be equal to the sum of Xiao Ming's and Dad's ages," we can set up the equation and solve it.
【Solution】Solution: Let $x$ be the number of years after which Grandpa's age will be equal to the sum of Xiao Ming's and Dad's ages. According to the problem, we have:
$$
\begin{aligned}
35+x+11+x & =60+x \\
2 x+46 & =60+x \\
x & =14,
\end{aligned}
$$

Answer: After 14 years, Grandpa's age will be equal to the sum of Xiao Ming's and Dad's ages.
Therefore, the answer is: 14.
【Comment】The equal relationship in this problem is clear, and it can be easily solved using an equation.