Answer: Choice C
Step-by-step explanation: The correct sum of 6 feet 10 inches and 8 feet 9 inches is 15ft 7 inches.
In order to calculate this, you will first add the inches.
10 inches plus 9 inches equals 19 inches, which is 1 ft 7 inches.
Next, add the feet - 6 ft plus 8 ft equals 14 ft.
To finish, 14 ft plus 1 ft 7 inches equals 15 ft 7 inches, which is choice c.