The correct option is C 15
In compound I, double bond takes maximum preference and hence when we number it, we can assign the number 6 to the carbon atom with Br.
In compound II, double bond takes maximum preference and hence when we number it, we can assign the number 3 to the carbon atom with Br.
In compound III, double bond takes maximum preference and hence when we number it, we can assign the number 1 to the carbon atom with Br.
In compound IV, double bond takes maximum preference and hence when we number it, we can assign the number 5 to the carbon atom with Br.
When we add all these locants, we get 15.