3. AB is a chord of the circle and its center is ?O?. ON is perpendicular to AB. If the length of AB=20 cm, ON-(2?11) cm, find the radius (in cm) of the circle.
7. ?ABC is similar to ?PQR. Length of AB is 18 cm and length of the corresponding side PQ is 12 cm. If area of ?ABC is 324 sq cm, what is the area of ?PQR?
9. In ?DEF, G and H are points on side DE and DF respectively. GH is parallel to EF. If G divides DE in the ratio 1:3 and HF is 7.2 cm, find length of DF?