If the simple graph G has 5 vertices and 7 edges, how many edges does G` have ? - If this was your question
with 5 vertices a complete graph can have 5c2 edges => 10 edges
We know that edges(G) + edges(G`)=10 so edges(G`)=10-7=3
Had it been
If the simple graph G` has 5 vertices and 7 edges, how many edges does G have ?
Then G would've had 3 edges