it is 18 for sure.

Sum of degrees of all vertices = twice the number of edges = 2e we know,

now e = n-1

here n = 10 given

hence 2e = 2(n-1) = 2*9 = 18

Sum of degrees of all vertices = twice the number of edges = 2e we know,

now e = n-1

here n = 10 given

hence 2e = 2(n-1) = 2*9 = 18