Hey!
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Formula: Distance / Time = Speed
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Solution:
Speed = 15/20 = 0.75cm/sec
Velocity = 5/20 = 0.25cm/sec
10 + 5 = 15 (distance traveled)
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Answer:
Speed = 0.75cm/sec
Velocity = 0.25cm/sec going forward.
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Hope This Helped! Good Luck!