Open Question: Calculate the visual angle (in degrees) for each of the following stimuli.?

Please tell me the formulas to each so that I learn them and can get the correct answers:
Calculate the visual angle (in degrees) for each of the following stimuli.

A person whose height is 2 m, standing 100 m away (m = meters).

The same person standing 200 m away.

A child whose height is 1 m, viewed from 100 m.

The same child viewed from 50 m.

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