You were good up to here:

But then things go awry:

Check your powers of ten - 5.9 billion Km is 5.9 x 10^9 Km, not 59 x 10^9. Similarly 1.5 billion Km is 1.15 x 10^9 Km. This error ripples through the subsequent lines.

How did you get the 4.481 x 10^21 term? It's probably just a typo, as 59^2 is 3481, not 4481.