Discrete Math

The following is is meant to have some assumptions made (like "n").  I have been up all night trying to figure this out. It can't be Euler because the vertices can't be >1. It might be Hamilton if I assume that E of G(V,E) is infinte..but how would I get my answer? I would just have sets (e1, e2,...)

Could this be a straight directed graph where I just count my vertices? If I substitute n for say...4, then I would have 4 vertices? therefore, 4 light are needed to be ordered? (sounds too simple)

Please help guide me in the right direction!


1. A contractor for a Paradise city on the XYZ planet has to order traffic lights for the  
    city. All streets in the city are straight and  infinitely long in both directions.
    No matter how many streets have the same crossing, there will be a need for only one    
    traffic light per crossing. Knowing only the number of streets n, how many traffic  
    lights will the contractor need to order to make sure he will not run out lights.