Hey guys, I am a new poster around here and I really can use a hand here!

I am in high school and I just cant do this one problem even though I have tried for hours...

So here's the deal, its a problem with 4 books and I need to find the prices for each one.

the clues are

- all the books without the 1st one gives a total of 42$

- all the books without the 2nd one gives a total of 40$

- all the books without the 3rd one gives a total of 38$

and

- all the books without the 4th one gives a total of 36$

Thank you for your time!

Any help or advices would be gladly appreciated!