Sense you do not have any options, this may be quite harder, But, I believe I got this. So, by looking at the following, it would look like the expression below:
We cant not use the numbers that are above to would give us 8. 2+9 would not equal 8 which would then show us that your answer may be the following:
The difference between the <span>highest and the lowest temperature is 9 because the highest number is 7 and the lowest number is -2 so the difference is 9.</span><span />