What would your estimate be for the mass of the object that the star is orbiting?

Suppose you observe a star orbiting the galactic center at a speed of 1500 in a circular orbit with a radius of 20.0 light-days.What would your estimate be for the mass of the object that the star is orbiting?1500 miles per hour, kilometers per hour, knots, feet per second, meters per second, miles per second, kilometers per second, or yard hertz per acre?