a) the temperature was -9 and now its 18
18 - -9 = 27
so it has risen 27 degrees.
if its easier add the 9 so it become 0 degrees than add the 18
so you end up with 9 + 18 = 27
b) -25 and 67
add 25 to get it to 0 degrees and now we only have to add 67 so it become a lot easier.
so 25 + 67 = 92