We consider the problem of multicasting sums over directed acyclic networks with unit capacity edges. A set of sources $s_i$ observe independent unit-entropy sources $X_i$ and want to communicate $\sum{X_i}$ to a set of terminals $t_j$. Previous work on this problem has established necessary and sufficient conditions on the $s_i - t_j$ 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 $s_i - t_j$ 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.