Answer:
9*sqrt(2) (third in your list of answer)
Step-by-step explanation:
Lets indicate the vertices with the letters beginning the upper vertice A next clockwise B and finally C (right angle)
Angle C=45 degrees. ANgle C is 90 degrees ( small square on the diagram means 90 degrees) So the angle A= 180-90-45=45 degrees.
Angle A=angle C=45 degrees=> AC=CB=9
Using Phitagor theorem will get AB= sqrt(AC^2+BC^2)=sqrt(81+81)=9*sqrt(2)
