We consider the problem of multicasting sums over directed acyclic networks with unit capacity edges. A set of source nodes si observe independent unit-entropy source processes Xi and want to communicate Σ Xi to a set of terminals tj. Previous work on this problem has established necessary and sufficient conditions on the si - t j connectivity in the case when there are two sources or two terminals (Ramamoorthy '08), and in the case of three sources and three terminals (Langberg-Ramamoorthy '09). In particular the latter result establishes that each terminal can recover the sum if there are two edge disjoint paths between each si - tj pair. In this work, we provide a new and significantly simpler proof of this result, and introduce techniques that may be of independent interest in other network coding problems.