Move the decimal so there is one non-zero digit to the left of the decimal point. The number of decimal places you move will be the exponent on the 10. If the decimal is being moved to the right, the exponent will be negative. If the decimal is being moved to the left, the exponent will be positive.
90 degrees means 90 degrees counterclockwise. So from the fourth quadrant we'll end up in the first quadrant. X and Y get swapped and one negated, it must be the -2 becoming 2, so our image is
