1.80 this. For the most common trapezoid AB < CD, AB= 10 AC= 15 BD=20, respectively, as the vertical lines AE and BF of CD, and the vertical feet E and F are within the line segment AB. Then ce = 9 ef =10fd =16cd =10+9+16 = 35, and the trapezoid circumference is 80.

2. If AE⊥CD point E is on the extension line of DC, then CD =10+16-9 =17, and the trapezoid circumference is 62.

3. If BF⊥CD and point F are on the extension line of CD, then CD= 10+9- 16=3, and the trapezoid circumference is 48.

I don't know if I made it clear. I have to draw a picture myself. I was going to draw with the geometric sketchpad, but it was not good. sorry