Systems of two linear equations in two variables SAT question

The correct answer is 30. Let x represent the number of correct answers from the player and y represent the number of incorrect answers from the player. Since the player answered 40 questions in total, the equation represents this situation. Also, since the score is found by subtracting the number of incorrect answers from twice the number of correct answers and the player received a score of 50, the equation represents this situation. Adding the equations in the system of two equations together yields . This can be rewritten as . Finally, solving for x by dividing both sides of the equation by 3 yields .