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 50 °F you have: ((50 + 459.67) × 5) ÷ 9 = (509.67 × 5) ÷ 9 = 2548.35 ÷ 9 = 283.15 K