Vancouver is a city on the north bank of the Columbia River in the U.S. state of Washington and the county seat of Clark County.
The width of the twin quilt is 66 +12 (for the two extra columns of 9 patches) + 4 (for the two extra strips of sashing) =82, which is a bit wider than your target of 78, but close enough. Plus, it's nice to have it a bit too large than a bit too small.
Twin over twin bunk beds are smaller than full over full models, and hold a twin-sized mattress on both the top and bottom bunks, which measures 3.25 feet by 6.25 feet. This is a size that can accommodate both children and average-sized young adults.