You can't, a SUM is the amount obtained as a result of adding numbers (18+7=25)18x7 is asking you to MULTIPLY the two numbers. This is call the PRODUCT of the two numbers (18*7 = 126).
The product is the result after multiplying a set of numbers or algebraic expressions
Adding two or more numbers together gives you a sum.
The result of adding two numbers is their sum.
The result of two numbers being divided together is called the quotient.
You'd call it a difference.
when you add two or more numbers together, the result is called the sum