The answer is negative because the greater number is negative whilst the other two numbers were not. And it is 22.6 because all three numbers together add up to be 22.6. So it being negative and 22.6 leads you to your answer. Also, -22.6 is greater than m because if -11.6 is greater than 6.7 and 4.3 +m then all three combined would definitely be greater than m.
