The question is attached in the image, with the given hint:
Add all the rows to the last. Factor out a common factor from the resulting last row, which will then become a row of 1’s. Subtract this row from all the previous rows.
This is confusing to me. I know you can change the rows of a determinant by adding multiples of other rows without changing the actual determinant, but the "factor out a common factor" part is throwing me. I don't have any real work to write down because I literally don't know how to start, so that would be helpful.