what math equation do you use to determine the number of stops darker in doors than outdoors if a photograph is properly exposed photograph is taken indoors at ISO 800, f/2.8, and at 1/50 of a second ?I have seen these 2 questions posted on another forum. It appeared to me that the question is a homework question rather something the poster really wanted to know. It it is the case how would the instructor taught the students to get answer to these kind of question. I know there are many ways to come up with the right answer but someone who teaches a photography class and put such a question in the homework how would that person teaches the students to solve the problem?Im trying to calculate sunny 16 rule and compare how much darker it is.

For instance if I do Sunny 16 rule on one picture

and use f2.8 ISO 640 and 1/50 second, is this how to calculate this?

f/16 is 5 times darker. And for reference I pick out 100, 1/1000.

5 times lighter for iso. and 4 times lighter for shutter. So it would be 4 times lighter?

I don't see 1/50 second for shutter speed though.