Answer:
c) 100,000 m/s
Explanation:
You need to take the same wave length from the top graph and bottom one, so let's take half a wave length then in the top one that is 0.005, but in the bottom one it's 2000/4 = 500 because they are smaller and there are 4 half waves before you get to 2000, whereas in the top one there is 1 half wave before you get to 0.005 on the graph.
Now use speed = distance / time
speed = 500 / 0.005 = 100 000 m/s
