I was on vacation in England, and wanted to visit the Tower of London. The roads were laid out on a grid map, and and the castle was 4 blocks north and 5 blocks east. I also wanted to visit the Apple store along the way, and check out the new IWatch.
If I were to travel only north and east, how many routes did I have to get to the castle?
See Part 1, Part 2, Part 4, and Part 5.