Let the number of Sociology books = y; the number of History books = x
⇒ x + y = 475 (2)
also since the number of history books sold was 83 less than sociology,
then x = y - 83 (1)
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.