How to find a sum of a number

There's no such thing as the sum of one number.  "Sum" is what you have
when you moosh two numbers together into one by adding them.

For example:

If you put 5 pennies into your pocket, and then later, you put 3 more pennies
into there, what's in your pocket now ?  Don't look, do it in your head. 
You said there are 8 pennies now. That's correct. How did you figure it out ?
You 'added'  5  and  3  and you got  8 .    8  is the 'sum' of  5  and  3 .

11/2.2 = 5 inches for the length 8.5/2.2= 3.86 inches for the width