To be sure understand it:
The locations of the masses on the rod below don't matter. All the total mass in all of the rods below (really all the weight) is in the string at the end of the current rod.
For rod b, you have 149*2 kg at x=0 cm. And 149 kg at x=65 cm. Divide by total mass (149 kg * 3).
For rod c, you have 149 kg * 3 at x=0 cm. And 149 kg* 1 at x = 65 cm. Divide by total mass (149 kg * 4).