Answer: 6ft
Explanation:
Since we are looking for the length that is parallel to the side with length of 16 we can use subtraction.
Imagine the entire shape as a rectangle. The side parallel should be equal to 16 since it would be the same length.
Therefore,
16 - 10 = 6
If we subtract a piece of the side from the full length of the side it will give us the missing piece. In this case 10 and 6 will make up the full length of 16. To clarify, the length of 4ft and 9ft make up the parallel side of 13 (4+9=13). We are applying this principle to the side of 16 as well.
Hope this makes sense! Let me know if you have any questions