Volume of liquid in a sphere.

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The second attachment is intermediate information that the CAS system gives you. Sometimes, the CAS system has to make assumptions to solve the problem and it tells you information about what it had to do. Usually, you can ignore this info. However, if you think there is an error, this info can sometimes give you a clue as to what might be going on.

Now, as to your solution, you should test any variable used to see what value it has in the CAS system. e.g. If you type r <enter> it should just show r (meaning that it has not been assigned a value). This means you can use it as a variable to solve for. However, if you use R, all the capital letters are assigned values in the Home system, so either change it to R1 or r and make sure it's not been assigned a value.