Answer:
The original dimension was 6 inches by 6 inches.
Explanation:
'x' represents the side measure of the original square photo.
Given is that Shayna enlarged a square photo by adding 10 inches to each side so it could be seen on a large poster.
The given equation is:

Solving for 'x' as x was the original dimension in which 10 was added.





and

Neglecting the negative value as dimension cannot be negative.
So, we have x=6 inch
Therefore, the original dimension was 6 inches by 6 inches.