What are some of the challenges for forensic scientists in dealing with fiber evidence?

A forensic scientist is a scientist who analyzes biological, chemical, or physical samples taken into evidence during a criminal investigation. It's their work to provide the proof the police need to bring the case to court. 

Also, forensic scientists examine contact trace materials associated with crimes in order to provide evidence for criminal investigations. The work is usually dealt with under three sections: biology, chemistry and drugs/toxicology. 

replace   c   with   a   and simplify.

a = c , b = a, q = n , 2 , a = c , 900 b= a , 700 , q = n , 600 , 2 = b o t h , b = a , q = n