You could use equivalent fractions. The original Antelope Canyon is 74" square and you want it to be about 110" square. that would make the 2 1/2" strips 3.716" wide and the 1 1/2" strips 2.229" wide. If you rounded up it would be 3 3/4" and 2 1/4". If you rounded down it would be 3" and 2".