383=54872 and 393=59319
55555 lies between them, so 355555 is between 38 and 39.
Quick estimate: 3N≈a+3a2N−a3, with a=38:
355555≈38+3×38255555−54872
=38+4332683
≈38+0.1577
=38.1577
This estimate is very slightly above the true value (by less than 0.001), so:
355555=38.157…
Rounded to two decimal places, 355555=38.16.