\[Рисунок\ в\ учебнике.\]
\[OA_{1} = A_{1}A_{2} = A_{2}A_{3} = A_{3}A_{4};\]
\[A_{1}B_{1} \parallel A_{2}B_{2} \parallel A_{3}B_{3} \parallel A_{4}B_{4};\]
\[OB_{1} = 3\ см.\]
\[1)\ B_{1}B_{2} = OB_{1} = 3\ см;\]
\[2)\ B_{2}B_{3} = B_{1}B_{2} = OB_{1};\]
\[OB_{3} = 3OB_{1} = 9\ см.\]
\[3)\ B_{3}B_{4} = B_{2}B_{3} = B_{1}B_{2} = OB_{1};\]
\[B_{1}B_{4} = 3OB_{1} = 3 \bullet 3 = 9\ см.\]
\[Ответ:\ \ 3\ см;\ 9\ см;\ 9\ см.\]