Whenever you're interested in computing the (absolute) difference between two values of a certain variable, you have to subtract the final value and the initial value. This is often written as delta:

So, in this case, the final temperature is -30°F. The initial temperature is 115°F. So, the variation is

A negative delta indicates that the value decreased, which is our case.
I believe that is it 100, since it is the only number listed that has factors and multiples.
Hope this helps!
1. Angle A is not 105degrees. As you can see on the horizontal line that it lies on, it's under 90degrees(acute). The angle aside from it is over 90degrees(obtuse).
2.Angle B is in fact not 75degrees.. By looking at the angle it's obtuse, over 90 degrees, so it can't be 75degrees.
Are 6 and 15 the legs of the triangle?