Transmission lines and superposition
It is actually valid, the way this question is worded, that the left and right side's reflection coefficient don't know about each other. This is because the time of interest expires after 120 ns.  As you computed, one leg is 40ns long, the other is 25ns. If you consider that the for one load to affect the reflection of the other the step voltage would have to travel round trip on one leg, (e.g. 2 × 40 ns) and round trip on another to get t point A twice (e.g. 2 × 25 ns), it would take 130 ns.  Therefore, an assumption of not considering the loads knowledge of each other is somewhat valid here as this effect happens 10 ns after the observation ends.

That is to answer about the multiple loads.  I'll leave the rest of your homework to you.