Answer
$$77 K = -321^{o}F$$
Work Step by Step
We know the temperature of liquid nitrogen is $-321^{o}F$ so 77 K must be equal to $-321^{o}F$.
To solve mathematically, convert Kelvin to Celsius and then Celsius to Fahrenheit:
$^{o}C = K - 273.15 $ is our first conversion factor. $^{o}C = 77K - 273.15 = -196.15^{o}C$
$^{o}F = 1.8(^{o}C) + 32 $ is our second conversion factor. $^{o}F = 1.8(-196.15^{o}C) + 32 = -321^{o}F$
