Which if the following sets if numbers could represent the sides if a triangle?
a. 5,6,13
b. 6,8,12
c. 7,7,15
d. 8,10,18

Try C.. that looks like its the right answer.. if not well then you learned a valuable lesson.. never trust me lol

The two smaller sides added together have to be bigger than the biggest side. 
Lets say A: 5+6=11 which is smaller than 13 thus it cannot be a triangle. 
Try this with all and you will know the answer.