How to calculate this 14 foot , 12 sheets, 760 , ?

It seems like there may be some missing information in your question.

If you are trying to calculate the total area of 12 sheets of material that are each 14 feet long and 760 units wide, you would first calculate the area of one sheet and then multiply by the number of sheets.

To calculate the area of one sheet, you would multiply the length by the width:
14 feet x 760 units = 10,640 square feet

Then, to find the total area of all 12 sheets, you would multiply the area of one sheet by the number of sheets:
10,640 square feet x 12 sheets = 127,680 square feet

If this is not what you were looking for, please provide more information so I can assist you further.