Use Dijkstra's algorithm to construct a graph that has 3^n shortest paths between a source vertex "x" and a sink vertex "y", where the number of vertices is a function of the form an + b for some natural number a,b. More precisely we need to prove: For every natural number n, there is an undirected graph of an + b vertices such that for some pair of vertices x, y in the graph, there are 3^n shortest paths from x to y.