Answer:
3 ft, 5ft, 6ft
Step-by-step explanation:
To build a kennel of my dog, I would try to make it the largest possible with what I have.
So, I would go with the 3 longest planks: 3ft, 5ft and 6ft.
By looking at the length, I see I could make something very close to a right triangle since I could use the 6ft as an hypotenuse, and have the two other sides as 3ft and 5 ft (6² is almost 3²+5², which equal 34).
That means my corner angle would be slightly over 90 degrees.