<h2><u>Direct answer</u> :</h2>
Width of the enlarged photograph = 14 cm
<h2><u>Steps to derive the correct answer</u> :</h2>Length of a small photograph = 6 cm
Width of a small photograph = 4 cm
Length of the photograph when enlarged = 21 cm
Let the width of the photograph when enlarged be x.
Which means :
Thus, the value of x = 14
Therefore, the width of the enlarged photograph = <u>14 cm</u>