Graph Algorithms · Challenge problem

A network has vertices $s,t,u,v,w,x$ and weighted edges $st{:}4, su{:}6, tu{:}2, tv{:}7, uv{:}3, uw{:}5, vw{:}1, vx{:}8, wx{:}2$. Running Prim's algorithm starting from $s$ (always adding the cheapest edge leaving the current tree), what is the TOTAL weight added to the tree at the moment vertex $w$ joins it (not the final total once every vertex is in)?