The increase in temperature can be calculated using the absolute value of the difference of the two numbers. The absolute value is the positive value of whatever is inside of the two symbols, | |.
We can check this by seeing that at midnight the temperature was -8, and at noon it was 23. Therefore, the temperature increased 23+8 degrees which is 31.
| -8-23 | = 31, which allows us to see that D is the correct answer
