Unsold books of store A is approximately is what percent more or less than total unsold books of store B and C together.

Unsold books of store A

$= 3500 imes frac{{80}}{{100}} = 2800$

Unsold books of store B and C together

$= 5000 imes frac{{60}}{{100}} + 4500 imes frac{{70}}{{100}} = 6150$

Required % = $frac{{6150 - 2800}}{{6150}} imes 100 = 54{ m{\% }}$