We can calculate the mass of a galaxy by observing how faststars are moving around its edge. Further we can estimate how manystars are in that galaxy using an average star mass of around 1/2solar mass. NGC 253 (image below) is a flat spiral galaxy with adiameter of about 60,000 ly. If a star on the edge of NGC 253 isobserved to have an angular velocity of about 7.8x10-16 rad/s, (a)calculate the mass of the galaxy and (b) estimate the number ofstars in it.
