Answer: The length of KM is 16.
In an isosceles trapezoid, the two non-parallel sides are congruent. Therefore, we have two options: either there are two 9's or two 6's in the trapezoid.
Let's try both options to find the length of the missing side:
40 - 9 - 6 - 6 = 19
OR
40 - 6 - 9 - 9 = 16
The only choice that is an option is 16.
