Could someone explain this to me????

Your answer would be 265 because knowing that the lowest temp is a negative number, and you're trying to find the difference between a positive number from a negative number, you would have to add a number to -129 to cancel it out and make it 0. The only number that would do so would be 129. Then by using 129, add 136 to it and you will get your answer, I hope this helps :)