Ratio of sold plain and lined books for store C is 5 : 4 and for store B is 3 : 2. Then find the total plain books sold by these two stores together?

Total books sold by store C = $45 imes 100 imes frac{{30}}{{100}}$

= 1350

Plain books sold by C = $1350 imes frac{5}{9} = 750$

Plain books sold by store B = $frac{3}{5} imes 5000 imes frac{{40}}{{100}}$

= 1200

Required number of books = 1200 + 750

= 1950