I have a test this coming week and I am currently studying for it, however I've become stuck on a few problems. I worked them out but according to the teacher's answers I got them wrong. Unfortunately, the teacher does not go into further detail about how he got his answers. Please help! Thanks.

1. A college bookstore marks up the price it pays the publisher for a book by 20%. If the selling price of a book is $84 how much did the book store pay for the book?

2. A builder of tract homes reduced the price of a model by 15%. If the new price is $186,660 what was the original price?

3. Erik has $18,300 to invest and decides to put some in a CD that earns 2.5% interest per year and the rest in a low stock that earns 2.6%. How much did he invest in each to earn $468.85 interest in the first year?