It is given in the question that
Anna buys 12 pens and 20 pencils for a total cost of $16. One pen costs $0.40 more than a pencil. 
Let the cost of pencil is $ x .
Therefore cost of pen is 

According to the question

Distributing 12 and combining like terms, we will get

Therefore cost of pencil is $0.35 and cost of pen is

 
        
             
        
        
        
Answer:
21 chickens
Step-by-step explanation:
10×4=40
82-40=42
42÷2=21