This piece of art would fall under the potrait category
Look at how this picture is similar to the one you are asking about.
Answer: you should use the topic: a scene featuring 2 characters sitting on the edge of a bridge
because: you could choose to make it a happy scene or a depressing scene or you can add two of the choices together and have two people together on a bridge and one is proposing to the other which may give you extra credit (depends on the teacher)
In decimal it would be -7.64423077