Basically, in math the "mean" is a set of numbers that you add, then take the sum and divide it by how many numbers are in that set. Here is an example: 6, 7, 4, 5, 8, 9, 3. The sum of the numbers in this set is 42. However, there are 7 numbers in this set. So basically what you would do is take the sum of the numbers, 42, and divide it by the amount of numbers that are in this particular set, 7. So, 42÷7=6. So now you have figured out that the mean is 6. I hope this could be helpful!
I dont know if this could help you but if you can please try to answer those two that I didn't complete so you could have an idea on what there relationships are and things like that.