How can these graphs be plannar? Is there a good way to prove it? I don't know how could I prove these graphs are plannar or not, the book does not give examples how to do so and i'm consufed.
Can someone show me how to do it? I'd appreciate


The graph 'a' is not planar since it contains the subgraph
$\{\{7,8\},\{1,8\},\{1,7\},\{2,7\},\{2,8\},\{4,7\},\{4,8\},\{1,2\},\{1,4\},\{2,4\}\}$
which is isomorphic to $K_5$, the complete graph with $5$ vertices.
https://en.m.wikipedia.org/wiki/Planar_graph
