Get twenty people, from various genders and ages, to be your testees. Create a random test that has both analytical and logical problems, and get the 'testees' (I have no idea if this is a word or not) to do the test before and after spending time outdoors.
An independent variable is how much time they spend outside, and the dependent is how well they function afterwards. (I think).
The constant is what stays the same, so most likely the tests in this case (if taking my example)
I don't really know what you mean by control, though...
This is what I would've done if it was my homework assignment, I'd suggest looking over my answers to see if they're accurate or not. Hope I helped, and good luck.
