The answer is the fourth option "difference of squares method." It's not the first option because the substitution method is when you pick one of the equation in a system of equations, solve it for a variable and then plug the variable into the other equation to help solve. It's not the second option because the graphing method is used to solve a system of equations by graphing the equations on the same coordinate plane, it's not the third option because the addition method is also known as the elimination method which is the third method to solving a system of equations. Therefore your answer is the fourth option.
