Answer:
1/3
Explanation:
To find the scale factor, divide a dimension in the new figure by the corresponding dimension in the original figure.
Figure B is a scaled copy of Figure A, so Figure A is the original figure, and Figure B is the new figure.
The side measuring 5 in Figure B corresponds to the side measuring 15 in Figure A.
scale factor = (length in new figure)/(length in original figure)
scale factor = 5/15 = 1/3