(a)    Stationery set  [40.60][11.90]  = 52.50                  Total cost = 93.10

         Files                   [40.60]                                              (93.10 – 11.90) / 2  = 40.60

       Hence cost of stationery sets = 40.60 + 11.90 = $52.50

(b)   Let u be the number of Stationery Sets bought,  So Files = 2u

        Unit Price of File = (40.60) / 2u =  (20.30)/u

        Unit Price of  Stationery Set = 2.30  +    (20.30) / u     (SS is $2.30 more than file)

       u  [ 2.30  +    (20.30) / u ] =  52.50             (number of SS x unit price of SS)

             2.30u  = 52.50 – 20.30 = 32.20

                  u = 32.20/2.30  = 14

Hence number of stationery sets bought was 14.

a) Cost of Files = (93.10-11.90)/2 = $40.60
   Cost of Stationery Sets = 40.60 + 11.90 = $52.50

b) We know: 1 Stationery - 1 File = $2.30.
   (Since there are twice as many Files as there are Stationery Sets,
   we should half it so that we can compare apple-to-apple.)
   Cost of Half the Files = 40.60/2 = $20.30
   Difference in cost = 52.50 - 20.30 = $32.20
   Count of 'Half the Files' = 32.20/2.30 = 14.
   So number of Stationery Sets is 14.

Note:
  In the 2nd diagram, height of a block represents the price of an item.
  Width represents the number / count of items. Thus area of a block
  represents the Price x Count = Cost of the items.

No algebra! :D