When solving a system by multiplying and then adding or subtracting how do you decide whether to add or subtract?

When solving a system of equations by multiplying and then adding or subtracting, you decide whether to add or subtract based on the coefficients of the variables you want to eliminate. If the coefficients of one variable are opposites (e.g., +3 and -3), you would add the equations to eliminate that variable. Conversely, if the coefficients are the same (e.g., +3 and +3), you would subtract one equation from the other to eliminate the variable. The goal is to simplify the system and isolate one variable for easier solving.