The most important information that needs to be kept in mind is the conversion from square foot to square inches. Other important information's are already given in the question.
1 square foot = 144 square inches
Now
Number of glasses required to cover 1 square foot = 8
Then
The number of glasses required to cover 144 square inches = 8
So
The number of glasses
required to cover 864 square inches = (8/144) * 864
= 8 * 6
= 48
So 48 pieces of glass are required to make a window that is 864 square inches. I hope the procedure is clear enough for you to understand.
