It is helpful to plot the points, then mentally test the answers for plausibility. Translation of E 1 unit to the right puts it at (2, 1), then rotation counterclockwise 90° about the origin puts it at (-1, 2), the location of E'.
The appropriate choice seems to be
A translation 1 unit to the right followed by a 90-degree counterclockwise rotation about the origin_____
Translation 1 unit right: (x, y) ⇒ (x+1, y)
Rotation 90° CCW: (x, y) ⇒ (-y, x)
Both transformations in that order: (x, y) ⇒ (-y, x+1)