The answer is 9.
We have been given that dimensions of original photo are 4 inches by 6 inches. We want the photo on the poster to be of dimensions 3 feet by 4 1/2 feet.
First of all we will convert dimensions of poster from feet to inches.
Now, let us compare sides of our original photo with corresponding sides of poster.
Now, let us compare the second pair of corresponding sides.
We have seen that sides of poster are 9 times the sides of our original photo, therefore, the scale factor of this dilation is 9.