[填空题]
Three cubes, of sidee3 pczkqzg.2 4;z e;wvf w713z2b5hkb tb0zhss $l_0$,$2l_0$, and $3l_0$ are placed next to one another (in contact) with their centers along a straight line and the $l=2l_{0}$ cube in the center (Fig. 7–39). What is the position, along this line, of the CM of this system? Assume the cubes are made of the same uniform material. $X_{CM}$ = $l_0$ from the edge of the smallest cube
