∑( 1≤k≤n)d(vi) = 2m (n is the number of nodes, m is the number of edges, and d(vi) is the degree of vertex vi).

Solvable:

1) According to the conditions, there are

2 * 16 = 2m =∑( 1≤k≤n)d(VI)= n * 2，

The number of solvable nodes n =.

2) According to the conditions, there are

2 * 2 1 = 2m =∑( 1≤k≤n)d(VI)= 3 * 4+(n-3)* 3，

The number of solvable nodes n =.

3) (for you)