*edit* can't upload images from phone with app for some reason, finding a computer. Using the app for the first time so hopefully this works out ok.. I've attached an image with the problem written in blue, and a complete attempt in gray. I have the answer to the question however it is completely different to mine.. Also, relevant equations are in the gray box on the right (the first line for each, the second is with the values subbed in). I think it's correct up until the line where I first get L[y] on its own. But I could be wrong..