Dear Student,
Celsius, also called centigrade, scale based on 0° for the freezing point of water and 100° for the boiling point of water. It is used as temperature scale.
The Kelvin is the base unit of temperature in the International System of Units, having the unit symbol K. It is used as temperature scale.
According to theory:
0 K = 273.15 oC
oC (Temperature in oC) = K (Temperature in Kelvin) - 273.15
(a) 50 K in oC = 50 - 273.15
= - 223.15 oC
(b) 390 K in oC = 390 - 273.15
= 116.85 oC.
Regards