sum = + - The term "sum" is used when adding. Therefore, it is equal to "+".
8 times a number and 2 = 8x + 2 - 8 is equal to 8. The term "times" is used when multiplying. Therefore, it is equal to "×". "A number" is a variable. A variable can be any letter. In this case, I have made it "x", which is commonly used.