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. As the royal baby was going to be in town, a large area was cordoned off and there was to be no traffic though.
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 3, and Part 5.