**1. The problem statement, all variables and given/known data**
Consider a system of two blocks that have masses m_1 and m_2. Assume that the blocks are point-like particles and are located along the x axis at the coordinates x_1 and x_2. In this problem, the blocks can only move along the x axis. Find the x coordinate of the center of mass of the system.

**2. Relevant equations**
The solution is (

, but I cannot for the life of me understand why this is exactly. Why multiply the mass by the x-coordinate of its location?

**3. The attempt at a solution**