Discrete structures - Double counting on graphs

Double counting on graphs 7 Prove using double counting that every 2-connected plane graph with v2 vertices and f faces in which every face has size at least 5 has that v3f/2+2. Here the size of a face is defined as the number of edges adjacent to it. You can use the following property without having to prove it In every 2-connected plane graph each edge is adjacent to two different faces