Final answer:
A 90º counterclockwise rotation turns an object left and a 90º clockwise rotation turns an object right. For the letter C, a counterclockwise rotation would make it look like it's lying on its back, while a clockwise rotation would turn it to appear as if it's standing on its head.
Step-by-step explanation:
The difference between a 90º counterclockwise rotation and a 90º clockwise rotation involves the direction in which an object is turned. If you imagine standing on a clock face, a counterclockwise rotation will move an object to the left (or in the reverse direction of clock hands), while a clockwise rotation will move it to the right (in the same direction as clock hands).
When using the letter C as an example:
A 90º counterclockwise rotation would make the letter C look like it is lying on its back with the opening facing up.
A 90º clockwise rotation would flip the letter C so it appears standing on its head with the opening facing down.