Cost of the MST of the graph
A Yuval said, you can just go ahead with any algorithm. In fact, you should probably be able to find a solution by trial and error. 

In case you are stuck for some time, move your mouse over to see a solution below.


   We can use Prim's algorithm, which iteratively selects an edge of the least weight from the available edges as long as it does not introduce a cycle.

 We will select the edge of weight 1, two edges of weight 2, all edges of weight 3,4,5,6,7 respectively. We will skip the vertical edge of weight 8 since it introduces a cycle. We will select the horizontal edge of weight 8. Now all vertices have been included except the bottom left one. So we will select the edge of weight 12 to connect vertex.

 The total weight is 1 + 2 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 12 = 50. So the answer should be "none of the listed".