The length of the enlarged photo would be 21 in.
For the original picture, we can represent the length as x and the width as x-3. Then we can use the perimeter equation: p=2w + 2l
22 = 2x + 2(x-3)
22 = 4x - 6
x = 7
Since the original length is 7 and the length is tripled, the new length is 21 in.