Graph Algorithms · Hard problem

A network connects towers $p,q,r,s,t,u$ with cables $pq{:}3, pr{:}5, qr{:}2, qs{:}6, rs{:}4, rt{:}7, st{:}3, su{:}8, tu{:}5$. If cable $rs$ becomes impossible to lay, by how much does the minimum total connection cost increase?