When should you use multiplication to solve a system of linear
equations by elimination

To use the elimination method you need the same variable in each equation to have the same coefficient. If neither variable has the same coefficient in each equation, you need to multiply one or both of the equations by a constant to get the same coefficient.

Step-by-step explanation:

Rule of Addition: The probability that event A or event B occurs is equal to the probability that event A occurs plus the probability that event B occurs minus the probability that both events A and B occur. Mathematically, it sounds

In your case,

so