Suppose you have 3 pieces of string measuring 6 inches, 9 inches, and 12 inches. how many unique triangles can you form with these pieces of string?

A triangle should have 3 points and 3 sides. Let say that the point is ABC. Then the sides would be AB, AC and BC.
There are 3 strings with a different length that can be put into the sides. Assuming the string can be used once, then the possible way would be:
3!/(1+3-3)!= 3!/1!= 3*2*1= 6 ways