The translation of pentagon PQRST eight units to the left will not change the length of any segments in the pentagon, including the length of Q'R'.
To find the length of Q'R', we need to consider the initial length of QR in pentagon PQRST. Since the translation does not affect distances between points, the length of Q'R' will remain the same as the length of QR.
As the specific lengths of the sides of pentagon PQRST are not given in the question, we cannot determine the exact length of Q'R' without additional information. However, since the answer choices are finite, one of them must reflect the unchanged value after the translation.
If you have the length of QR from the original pentagon PQRST, that will directly give you the length of Q'R'.
If we're working with the assumption that the original length is one of the given options (6, 4, 5, or 3 units) then the length of Q'R' must also match the originally measured length of QR.
In summary, without the original dimensions, we cannot definitively answer which of the options is correct. If you happen to know the original distance of QR, that would provide the answer for Q'R'.