How to answer this Trig question...?

[brinazarski]

http://i158.photobucket.com/albums/t120/brinazarski2/hw75.png

Number 21. Apparently, the answer is 24.08. I have no idea why that's the answer, and I checked over my work and could find nothing wrong (I got 16.88). Obviously I'm doing SOMETHING wrong. Could someone explain how to get the answer to that question?

 

[tkhunny]

No need to get stressed. Go very calmly. You are given the angle between them when subtracting. What is the angle between them when adding? Hint: Move the 18 to the other end of the 12.

Additional Hint: 180º - 75º = 105º