Task: Question Answering
Input (English): Baking a Birthday Cake For an Awesome Nephew It was the day before my nephew 's third birthday . I wanted to bake him a very special birthday cake . He loves tractors and anything related to farms , so I wanted to include that when I decorated the cake . I decided to make a cake with three layers since he was going to be three years old . I started by finding recipes for both chocolate and yellow cake since I knew that those were his favorites . I made the batter for the chocolate cake in one bowl and then the batter for the yellow cake in another bowl . I poured some chocolate cake batter in the largest and the smallest round baking pans since the top and bottom layers would be chocolate . I poured yellow cake batter in the medium-sized round baking pan since it would be the middle layer . I baked all three cakes and then cooled them . After they cooled , I stacked the cakes according to size and I frosted the bottom and top layers with yellow frosting and the middle layer with green frosting . I decorated the top of the cake with farm animals , a small toy tractor and the words , '' `` Happy Birthday Samuel . '' '' I topped off the cake with a number 3 candle . My nephew was very happy when he saw the cake . He was very surprised that I had baked a cake for him . 
Question: Why were they celebrating with a cake?
Output (English): Samuel's 3rd birthday