To convert degrees Fahrenheit to Kelvins you need to add 459.67 to degrees Fahrenheit multiply the result by 5 and divide it by 9.
With 6 °F you have: ((6 + 459.67) × 5) ÷ 9 = (465.67 × 5) ÷ 9 = 2328.35 ÷ 9 = 258.70555555556 K