Answer: 137 history books were sold
80 chemistry books were sold
Explanation:
Let x = the number history textbooks sold by the textbook store in that week.
Let y = the number chemistry textbooks sold by the textbook store in that week.
The textbook store sold a combined total 217 of history and chemistry textbooks in the week. This means
x + y = 217 - - - - - -1
The number of chemistry textbooks sold was 57 less than the number of history textbooks sold. This means
x = 57 + y
Substituting x = 57+ y into equation 1. It becomes
57+y+y= 217
57 + 2y = 217
2y = 217 - 57 = 160
y = 160/2 = 80
x = 57 + y = 57 + 80
x = 137
137 history books were sold
80 chemistry books were sold