Answer:
15
Explanation:
Equation to remember:
Length · Width · Height = Volume
LWH = V
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In this word problem, you can find that we're missing the height aspect of the equation. Your equation would look something like this:

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Work:

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As you can see, the height of our rock is 15cm.
I hope this helped!
Sincerely,
Your Friendly Neighborhood
Middle School Math Teacher!