Concept:To find the length of the third piece, we subtract the lengths of the two known pieces from the total length.Explanation:We are given the total length of the glass rod and the lengths of two of its pieces. We need to find the length of the third piece.1. Total length of the glass rod = $32.75$ cm.2. Length of the first piece = $7.05$ cm.3. Length of the second piece = $12.325$ cm.Let the length of the third piece be $x$ cm.The sum of the lengths of the three pieces must equal the total length of the rod.So, $7.05 \text{ cm} + 12.325 \text{ cm} + x \text{ cm} = 32.75 \text{ cm}$.First, let's add the lengths of the two known pieces:$7.05 + 12.325 = 19.375$ cm.Now, we can find the length of the third piece by subtracting this sum from the total length:$x = 32.75 - 19.375$$x = 13.375$ cm.Answer:The length of the third piece is $13.375$ cm.