554.590:90

Interpreting as a ratio 554.590 : 90:

• Convert to a decimal: 554.590 / 90 = 55459 / 9000 ≈ 6.162111111...
• As an exact integer ratio (simplified): 55459 : 9000
• Decimal form: 6.162111111... (the 1 repeats)

If you want a 3-decimal approximation: 6.162.