Question

An object is placed in front of a concave mirror, 16.0 cm from the mirror's focal point. The image formed by the mirror is two times farther away from the focal point. Calculate the focal length of the mirror.
There are actually two possible image distances di that satisfy the statement of the problem. Enter the larger of the two image distances.
Enter the smaller of the two image distances.

To answer this problem since it provided the magnification and do I used the formula: m= -di/do to get the value of di
so I said 2= -di/16 therefore I said di=-32 I figured that would be the smaller value and the larger value would be +32 but that was marked wrong.
Also to get my focal point I used the formula: 1/f= 1/di + 1/do and I also got 32 as the answer but that was also marked wrong. What am I doing wrong?