Sally enjoyed the prospect to assemble data from the standing waves in a spring. She and her partner held the ends of spring 4.0 meters apart. There were 5 nodes in the standing wave formed. Sally moved her hand from the rest position back and forth all along the floor 20 times in 4 seconds. Determine the speed of the wave Sally formed?

i) 0.4 m/s

ii) 2.5 m/s

iii) 10 m/s

iv) Cannot be determined