Hi there!
The sum is the result you get by adding numbers together.
Twice "x" = 2x
The sum of 2x and 5 is 11
Your equation: 2x + 5 = 11
subtract 5 from each side of the equation
2x = 6
divide each side of the equation by 2
x = 3
There you go! I really hope this helped, if there's anything just let me know! :)