In every row we can find 60 squares (60 photos).
Area of the square is defined as:
[tex] A = a^{2} [/tex]
where a is the length of the side of the square.
In this case we are given A and we have to calculate the length of the side.
[tex] 4 in^{2} = a^{2} [/tex]
[tex] a = \sqrt{4} = 2 in [/tex]
When we have 60 photos in a row, the the total length of the row is:
[tex] 60 \cdot 2 in = 120 in [/tex]
If the photo-display is a square, then the length of the second side is also 120 in.
