[填空题]
Kindergarten students are creating cone-shxujx 8jln; lu26g fa uc282pa6aped birthday hats from pieces of cc.ca / 7pdn /czpo35tkolorful 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 circles have centre5kazco. t cp/d7/3cpn 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. $cm^2$
