One vertex sub-graphs: 4C1 (number of ways of picking one vertex among the four)
Two vertices sub-graphs: 4*2^1 (whether to include the edge available between the given selected set of vertices) + 2 * 1 as there is no edge between these set of vertices.
Three vertices sub-graphs: 4C3 * 2^2 (two edges incident on the any selected 3 vertices, 2^2 different ways of having/not-having these edges in the sub-grah)
Four vertices sub-graphs: 4C4 * 2^4 ( four edges)
Total number of subgraphs: 4 + 10 + 4C3 * 2^2 + 4C4 * 2^4 = 46