Answer:
There were 194 math textbooks and 129 Psychology textbooks sold
Step-by-step explanation:
Lets write some equations where M=math books and P= psych books:
1) M+P=323
2) P=M-65
1) Substitute M-65 as P in the first equation:
M+M-65=323
2) Combine alike terms:
2M-65=323
3) Add 65 to both sides:
2M=388
4) Divide both sides by 2:
M=194
5) Now, substitute 194 as M in the second equation:
P=194-65
6) Subtract:
P=129