How Many Vertices Does a Planar Graph with Degree 4 and 10 Regions Have?

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intelli
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i need some hints on how to do this problem

If a connected planar graph with n vertices all of degree 4 has 10 regions, determine n
 
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Use Euler's formula: v-e+f=2. The problem is to find e (the number of edges). Here you must connect the degree of each vertex with the total number of edges...