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The diagram shows a sector \(A O B\) of a circle with centre \(O\) and radius \(r \mathrm {~cm}\). The angle \(A O B\) is \(54 ^ { \circ }\). The perimeter of the sector is 60 cm .
- Express \(54 ^ { \circ }\) exactly in radians, simplifying your answer.
- Find the value of \(r\), giving your answer correct to 3 significant figures.