Answer: 14 (14.4 if your allowed to make 2/5 of a necklace)
Explanation:
First let's change the 6 yards of string to inches to make this easier.
Note: for every 1 yard it is equal to 36 inches
So let's multiply the length (6 yards) by 36 = 216 inches
We know that she needs 15 inches to make one necklace. So let's take our 216 inches and divide by 15.
216/15= 14.4
So Jenna can make about 14 necklaces.