I believe it is the final sentence: I left for college when I was 18 (that was also the age at which I was married). This is because the parentheses also give information about another incident that took place at the time - his/her marriage.
Let the price of single algebra book = x
and the price of geometry book = y
Then equation (1) = 2x+3y=34
3y= (34 - 2x)
y= (34 - 2x)/3
And equation (2) = 3x + 2y=36
put value of y in equation (2)
3x + 2 (34-2x)/3= 36
9x + 2 (34-2x)=108
9x + 68 - 4x=108
5x=40
x=8
put x=8 in equation ( 1 )
2(8) + 3y= 34
16+3y=34
3y=18
y=6
Hence, price of algebra book = 8$ and price of geometry book=6$
The authors purpose suggested by the text is explain how to use the guitar because it's not trying to convince you to buy a guitar and it isn't teaching you about all the parts on the guitar just how to tune the strings. Hope you found this helpful!
