Answer:
219 hairpins.
Step-by-step explanation:
Let, Jasmine has
hairpins.
Number of hairpins of Molly = 
As question said, Molly and Landy have 678 hairpins together.
We have calculated that Molly have
hairpins.
So, the number of hairpins of Landy = 
Now,
Landy and Jasmine have 984 hairpins together, so we can write from the above as,





It means, Jasmine has 765 hairpins.
Since Jasmine and Landy have 984 hairpins together.
So,
Number of hairpins of Landy = 984 - 765 = 219
So, Landy has 219 hairpins.