Sophat is 51 years old, and Rasmei is 21 years old. In how many years will Sophat be twice the age of Rasmei?

1. Problem Description

Sophat is 51 years old, and Rasmei is 21 years old. In how many years will Sophat be twice the age of Rasmei?

2. Solution Steps

Let $x$ be the number of years until Sophat's age is twice Rasmei's age.

In $x$ years, Sophat's age will be $51 + x$, and Rasmei's age will be $21 + x$.

We want to find $x$ such that:

$51 + x = 2(21 + x)$

$51 + x = 42 + 2x$

$51 - 42 = 2x - x$

$9 = x$

Thus, in 9 years, Sophat's age will be twice Rasmei's age.

3. Final Answer

9