Explanation:
This composition forms a rotation. It is a rotation of 90 degrees about pt E.
This is proven as D goes to D'' by the original rotation of 90 degrees and translation 1 unit up and as D'1 is the rotation of D about pt E by 90 degrees. We can see that D'' and D'1 lie on top of one another no matter how you move things around and are thus the same. Therefore a composition of a rotation of 90 degrees and a translation 1 unit up = a rotation of 90 degrees about pt E.