Final answer:
To find out how many more pieces of the shorter ribbon Eudora needs, subtract the number of pieces she already has from the total number of pieces she needs.
Step-by-step explanation:
To find out how many more pieces of the shorter ribbon Eudora needs, we need to know how many pieces she already has. If she needs a total of 12 pieces and she already has, say, 5 pieces, then she would need 7 more pieces (12 - 5 = 7).