6. (7 points) This year, Xiao Xiang, his father, and his mother's ages are 5 years, 48 years, and 42 years, respectively. $\qquad$ years later, the sum of his father's and mother's ages will be 6 times Xiao Xiang's age.
【Analysis】Suppose in $x$ years, the sum of Dad's and Mom's ages is 6 times Xiaoxiang's age, then: Xiaoxiang's age in $x$ years $\times 4=$ Xiaoxiang's Dad's age in $x$ years + Xiaoxiang's Mom's age in $x$ years, set up the equation and solve it.

【Solution】Solution: Suppose in $x$ years, the sum of Dad's and Mom's ages is 6 times Xiaoxiang's age,
$$
\begin{aligned}
(5+x) \times 6 & =48+42+2 x \\
30+6 x & =90+2 x \\
4 x & =60 \\
x & =15
\end{aligned}
$$

Answer: In 15 years, the sum of Dad's and Mom's ages will be 6 times Xiaoxiang's age.
Therefore, the answer is: 15.