This question is about an actual satellite (The Upper Atmosphere Research Satellite) that stopped functioning, and then fell back to earth on Sept. 23, 2011. The following table shows the satellite's altitude above the earth at the end of its fall. Day 55 is Sept. 23. Days 0 through 46 are not shown. Rows are numbered for convenience.

Find the average (vertical) velocity of the satellite between Day 54.5 and Day 55. Enter your answer as an exact fraction, no simplification required.
average vertical velocity = ____ kilometers per day

Hint: A negative velocity means that the satellite's altitude decreases as time increases.