What types of visual art mediums are heavily based on observation?

By adding two hours to 6:30, you get 8:30, then add the remaining 18 minutes to get 8:48 PM.

Then for the second one, subtract 8:30 from 2:00 to get an elapsed time of 6 hours. We check this by adding 6 hours to 2:00, and we see it gets us to 8:30 PM.

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