Final answer:
To solve this problem, represent the number as x. The sum of the number and three can be written as x + 3. Set up an equation and solve for x.
Step-by-step explanation:
To solve this problem, let's represent the number as x. The sum of the number and three can be written as x + 3. According to the statement, twice this sum is equal to eighteen, so the equation becomes 2(x + 3) = 18. Let's simplify this equation to find the value of x.
Learn more about Solving equations with unknown variables