So we want to know what is the sum of 6 feet 10 inches and 8 feet and 9 inches. To know that we need to know that there are 12 inches in one foot. So lets do the calculation. 6 feet + 8 feet = 14 feet. 10 inches +9 inches = 19 inches or 1 foot and 7 inches. We add 1 foot to our 14 feet and get the result: 15 feet 7 inches.