304 would be the correct answer
Step 1: Convert
, which is in radians into degrees. To convert it multiply by 

900/12
75
Step 2: 75 degrees isn't on the unit circle but 45 degrees and 30 degrees is. Since 45 + 30 = 75 you can use the cosine of 45 and 30 to find the exact value
cos45 = 
cos30 =
Step 3: Add the cos45 and cos30 to get cos5pi/12

Hope this helped!
1. $.0999 = $.1
2. $2.0192 = $2.02
3. $21.5953 = $21.60
4. $35.6667 = $35.67
5. $1.3999 = $1.40
6. $25.3333 = $25.33