When an edge lies inside a region, it contributes "2" to the degree of the region it lies within.

Degree of a region is the no.of edges on the boundary.

Degree(region 2)=ab+bc+cd+ad+de+de

Edge de lies in region 2 and contributes 2 to the degree.

So, deg of R2=6.

Degree of a region is the no.of edges on the boundary.

Degree(region 2)=ab+bc+cd+ad+de+de

Edge de lies in region 2 and contributes 2 to the degree.

So, deg of R2=6.