If the tiles are 2ft wide and the walkway is 2ft wide, then
the walkway is just a string of single tiles.
The walkway is 60ft long, so it needs
(60ft) / (2 ft/tile)) = 30 tiles.
They come in boxes of 6, so you need
(30 tiles) / (6 tiles/box) = 5 boxes.
Better get one more box, in case you break a few tiles.