For the first one:
1) Extend QRS to point T on the circle.
2) By the "power of a point": QP2 = QR·QT ---> 62 = 3·QT ---> QT = 12
Since QR = 3, RT = 9.
Since RS = 3, ST = 6.
3) Draw OT and OR, creating triangle(TSO) and triangle(RSO).
OT and OR are radii; Let the radius = r.
4) Use the Law of Cosines on these two triangles.
OT2 = r2 = 62 + 22 - 2·6·2·cos(TSO)
OR2 = r2 = 32 + 22 - 2·3·2·cos(RSO)
Since these are equal: 62 + 22 - 2·6·2·cos(TSO) = 32 + 22 - 2·3·2·cos(RSO)
40 - 24·cos(TSO) = 13 - 12·cos(RSO)
Since angle(RSO) is supplementary to angle(TSO), cos(RSO) = - cos(TSO)
---> 40 - 24·cos(TSO) = 13 + 12·cos(TSO)
27 = 36·cos(TSO)
0.75 = cos(TSO)
5) Since OT2 = r2 = 62 + 22 - 2·6·2·cos(TSO)
---> r2 = 40 - 24·0.75
r2 = 22
r = sqrt(22)