SOLUTION: Hi John paid $118.40 for 40 books and pens. He sold 6 pens. Then the same number of pens and books left. Each book costs 80 cents more than each pen. How much did he pay for the

Total books plus pens is 40.

Take off 6 pens from 40 items - you will get 40-6 = 34 pens plus books,
and there is the same number of books and pens in 34 items.


Hence, there were 17 books and 17+6 = 40-17 = 23 pens in the original collection.


Let x be the price for the book, in dollars.
Then the price for the pen is (x-0.8) dollars.


Now write the total money equation

    17x + 23(x-0.8) = 118.40.


Simplify and find x

    17x + 23x = 118.40 + 23*0.8

       40x    =      136.8

         x    =      136.8/40 = 3.42 dollars.


Thus, John paid  17*3.42 = 58.14 for the books.    ANSWER