How Do You Solve These Astronomy Homework Problems?

[PhysicsMajor86]

I cannot figure out the answers for the following problems:

1) If a star has a parrallax of 0.016 second of arc and an apparent magnitude of 6, how far away is it, and what is its absolute magnitude?

7) If a star is 10 times the radius of the sun and half as hot, what will its luminosity be?

13) If the orbital velocity of the eclipsing binary in Figure 8-17 is 153 km/s and the smaller star becomes completely eclipsed in 2.5 hours, what is its diameter?

 

[mgb_phys]

1, A star at a distance of 1 parsec has a parallax of 1 arc second.
Calculating absolute magnitude is explained very well here http://en.wikipedia.org/wiki/Absolute_magnitude