Question

A box contains two red balls, four green balls, and two white balls. You extract balls from the box with replacement 100 times. Eachh time you extract a red ball, you win $1; a green ball, you lose $0.50; a white ball, nothing happens.
-Make a box model of the net gain each time you play
-What is the expected value?
-By how much money will you be off the expected value?

I don't understand the box model part, but I drew a box with all the balls labeled with a color.
Then for expected value, I found the average: [$1(2)+$0.50(4)+$0(2)]/8 = 1/2. I know you plug it into the expected value equation but I'm notsure if the average is right.
I know to find how much money I will be off the expected value (aka find SD and SE).

I just need to know how to do the box model and if my average value is correct.