Formula:

* C = (F - 32) * 5/9

Where:

* C = Temperature in Celsius

* F = Temperature in Fahrenheit

Calculation:

1. Subtract 32 from the Fahrenheit temperature: 90 - 32 = 58

2. Multiply the result by 5/9: 58 * (5/9) = 32.22 (approximately)

Answer: 90 degrees Fahrenheit is approximately 32.22 degrees Celsius.