What is the sum of 6 feet 10 inches and 8 feet 9 inches?
a. 15 ft. 7 in.
b. 15 ft. 19 in.
c. 13 ft. 19 in.
d. 14 ft. 7 in.

Let us count up the feet first, then the inches.

First, we must know that 1 foot = 12 inches

6+8 = 14

Now the inches.

10+9 = 19

19-12 = 7

14+1 = 15

Final  15 feet, 7 inches

♥ Sum means addition
Add the Feet and Inches
6+8 = 14 feet
10+9 = 19 inches
Now since 1ft=12 ft then we have to use that to solve for our formula:
14+1 = 15 feet
19-12 = 7 inches 
 A. 15 ft. 7 in.

The length is 23 and y because you add them together