The given undirected graph is a complete graph on 10 vertices,so no of edges in Minimum spanning tree = 9
An edge is included in MST iff it's cost is less than or equal to the weights of the remaining edges and doesn't form a cycle,
Now,the minimum possible weight is 4 because it is a simple graph,so loops are not allowed.
Now,if we consider edges,(1,2),(2,3),(3,4),(4,5),(5,6),(6,7),(7,8),(8,9),(9,10),we obtain the required 9 edges each with a cost of 4
So,Total cost in MST = 9*4 = 36