Number of hyperconjugative structures in aromatic systems

I know that to find the number of hyperconjugative structures in aliphatic systems we use the formula $a + 1$ (where $a$ is the number of α-hydrogens in that compound) 


However, my teacher answered to the above question as: 



> 
> No, this formula is not valid for aromatic systems. 
> 
> 
> 


Why is it so? What is the exact formula? Is it that we don't count its original structure as a hyperconjugative structure? 


