Answer: 154
In one side of the glass window measuring 3 ½ feet, we can make (3.5/.25) exactly 14 pieces of a ¼ foot.
The other side of the glass window which measures 2 ¾ feet we can produce (2.75/,25) or 11 pcs of a ¼ foot.
The artist used (14*11) or 154 colored squares.