You are running a long, time-consuming simulation on a multicore server that is heavily used by all the engineers in your design group. Wanting to make optimal use of this shared resource, you make some measurements to determine how many cores your simulation can effectively use. You find that one run of your program takes 36 hours to run on 2 cores and 15 hours to run on 8 cores. How many cores should you specify for your program to use, and how long will one run take on that number of cores?