Managed to get two marks but dont know what else to add...
Does this help???
If you were the original poster, I'm not sure what to add
Maybe you should show the working of these stages:
1 Find the midpoint of AB, and thus, the coordinates of point D.
2. Find the midpoint of AC, and thus, the coordinates of point E.
3. Calculate the slope of DE.
4. Calculate the slope of BC.
Show how you find each of those things.
Then, at the end, add the same concluding sentence which you have written.