[填空题]
Kindergarten students are creating cone-shaped bz;pay)ov msd s5m4 (z 8:fojf,irthday zr60 +6ug8 ozay xt ,ytc9vs,zbn9h2y hats from pieces of colorful paper circles. The first step is to cut out a sector of the paper, as illustrated by sector OABC in the diagram below. The paper+syo9t zg9z , ,thcyyb6z an uvr06x28 circles have centre O and . The length of arc ABC is $4\pi$ cm and angle $\mathrm{A}\hat{\mathrm{O}}\mathrm{C}= \dfrac {2\pi} 7$
1.Find the radius of the paper circles, r. cm
2.Find the area of the sector the students cut out, OABC. $cm^2$
