To show that the rectangle in Quadrant III is congruent to the rectangle in Quadrant I, Darnell rotates the first rectangle 90 degrees clockwise into Quadrant II What is his next step?

Translate by what?

To complete the congruence between the rectangle in Quadrant I and the rotated rectangle in Quadrant II, Darnell needs to translate the rotated rectangle by a vector that moves it to Quadrant III.

The translation vector would be (x, y), where x represents the horizontal distance and y represents the vertical distance needed to move the rectangle from its current position in Quadrant II to Quadrant III. The values of x and y would depend on the dimensions of the rectangles and the position of their corresponding vertices.

Without specific dimensions or further information, it is not possible to determine the exact translation vector.