If Leda baked 73 cupcakes and accidentally drops 5. She has 68 left.
73 - 5 = 68
If she divides them in equal container she would have 3 left. 
13 x 5 = 65
Therefore: 68/15= 5 r 3
Therefore Leda had 5 cupcakes in each container and 3 left. 
Answer: 3 cupcakes