You made an algebra mistake near the end:

-5.23 = -2.5 log(x)

is okay, but then you wrote

log(x) = -2.5/-5.23 = 0.478 WRONG!

Instead,

log(x) = (-5.23)/(-2.5) = 2.092

So

x = 10^(2.092) = 124

So the star has 124 solar luminosities,
using the starting values you provided.
That's good: a difference of exactly 5 magnitudes
corresponds to a factor of 100 in brightness,
so this is about right.


Michael Richmond