Give an example of a graph with regions consisting solely of squares (regions bounded by four edges) and hexagons, and with vertices of degree at least 3. Write an expression for the sum of the degrees of the vertices (=2e) in such a graph in terms of v and s. the number of squares. Then use Exercise 17 to get an upper bound on 2e. Deduce that any graph of the sort defined in part (a) has at least six squares. If each vertex has degree 3, show that any graph of the sort defined in part (a) has exactly six squares.