a) We can use the equation for tangential speed:
TangentalSpeed = AngularSpeed * radius = 1.1 x 10-15 rad/s * 2.1*10^4 light years * 9.5 x 10^15 m
TangentalSpeed = 219,450 m/s
b) Then we can use the equation relating force to mass and velocity:
Force = mass * velocity^2/radius = 1.36 x 10^30 kg * (219,450 m/s
)^2/ (2.1*10^4 light years * 9.5 x 10^15 m)
Force = 3.28 * 10^20 N