Graph Algorithms · Medium problem

A weighted graph has vertices $s,a,b,c,d$ and edges $sa{:}6, sb{:}2, ab{:}3, ad{:}5, bc{:}4, cd{:}2$. A brand-new direct road $sd$ is built with weight $7$. By how much does the shortest-path distance from $s$ to $d$ decrease because of this new road?