Patterns with X and O

This task is about continuing a pattern and finding a rule.
a)
Draw in the next arrow in this pattern.
 

 
b)
 
Complete the table showing the number of O's and X's in the arrow pattern.
 

 

Number of O's 3 5 7    
Number of X's 3        
Total number of O's and X's 6        
 
c)
  
Complete the following sentence.
 
"To find the total number of X's and O's in an arrow, multiply the number of O's by "