We can find the scale factor by comparing the corresponding side lengths of the original rectangle and the enlarged rectangle.
The original rectangle has side lengths of 9 inches and 5.4 inches.
The enlarged rectangle has side lengths of 3 inches and 5 inches.
To find the scale factor, we can divide the corresponding side lengths:
(3/9) = 1/3
Therefore, the scale factor used to enlarge the rectangle in the image is 1/3, or approximately 0.33 as a decimal.