Let the number of Sociology books =Â y; the number of History books = x
⇒ x + y = 475  (2)
also since the number of history books sold was 83 less than sociology,Â
then x = y - 83Â (1)Â Â
BY substituting (1) into (2)
⇒ (y - 83) + y = 475
         2y = 475 + 83
          y = (558 ÷ 2)
          y = 279
⇒ x = 279 - 83
   x = 196
∴ Number of History books is 196 & number of Sociology books is 279.