To find the length of each piece of string after Emma cuts the 75-foot long string into 12 equal pieces, you can divide the total length by the number of pieces.
\[ \text{Length of each piece} = \frac{\text{Total length of string}}{\text{Number of pieces}} = \frac{75 \text{ feet}}{12} \]
Calculating that gives:
\[ \frac{75}{12} = 6.25 \]
So, each piece of string is 6.25 feet long.