what’s the length of the middle segment ?

Answer:
AB = 15
Step-by-step explanation:
I am assuming this is a trapezoid. The length of the mid-segment of a trapezoid can be found by taking the average of the two parallel sides, in this case, VW and UX.
The average is found by adding the total values and dividing by the number of values, which in this case, is 2.
9+21 = 30
30/2 = 15
AB = 15