Let L represent an arbitrary number. The phrase "The sum of a number and 12" may be translated as: L+12. If the sum of a number and 12 is -31, then the following equation is stated:
[tex]L+12=-31[/tex]Substract 12 from both sides of the equation:
[tex]\begin{gathered} L=-31-12 \\ \Rightarrow L=-43 \end{gathered}[/tex]Therefore, the number we were searching for is -43.
