Answer:
x = 3
Step-by-step explanation:
Because the endpoints of the segment with length 12.5 are the midpoints of the sides of the large trapezoid, the length of that segments, 12.5, is the average of the lengths of the top and bottom lengths of the large trapezoid.
(3x + 1 + 15)/2 = 12.5
Multiply both sides by 2.
3x + 16 = 25
3x = 9
x = 3
