adding HW6
Revert "remove HW4.ipynb"

This reverts commit 84cfcf0881d3de1c6703a175c654320e1d81892f.
Revert "remove HW3.ipynb"

This reverts commit ab8cffa561a7c491bad86fd331c2824376cca1d6.
Revert "remove HW1.ipynb"

This reverts commit c0d70bbd869cb517bcce01a34a58134a9687abfe.
Merge pull request #107 from dgergel/HW6_branch

Hw6 branch