For more like this go to https://www.letsdomath.ca/
It's an easy-to-use route to resources, faster than scrolling through videos on YT!
When you're great at finding the volume if you know the length, width and height, this is the next step. You'll be given the volume and 2 measurements and you have to find the third.
Here's a clear demonstration of what to do and why it works. It's short and to the point, and you will be successful with this method.