Concept:Form equations from given relationships and solve for the shortest piece's length.Explanation:Let the longest piece be L, the middle piece be M, and the shortest piece be S.Given: L=3M and S=L−23.Total length: L+M+S=40.Substitute L=3M and S=3M−23 into the total equation:3M+M+(3M−23)=407M−23=407M=63M=9 cm.Then L=3×9=27 cm, and S=27−23=4 cm.Answer:The shortest piece is 4 cm.