Answer
a) $-268.94^{\circ}C$, $-452.09^{\circ}F$
b) $204^{\circ}C$
Work Step by Step
a) Converting temperature from Kelvin to Celsius, we use the formula
$$T(^{\circ}C)=T(K)-273.15$$
Substituting,
$$T(^{\circ}C)=4.21-273.15$$
$$T(^{\circ}C)=-268.94^{\circ}C$$
In converting from Celsius to Fahrenheit, the formula is
$$T(^{\circ}F)=\frac{9}{5}\times T(^{\circ}C)+32$$
Substituting,
$$T(^{\circ}F)=\frac{9}{5}\times (-268.94)+32$$
$$T(^{\circ}F)=-484.092+32$$
$$T(^{\circ}F)=-452.09^{\circ}F$$
b) In converting from Fahrenheit to Celsius, the formula is
$$T(^{\circ}C)=\frac{5}{9}\times(T(^{\circ}F)-32)$$
Substituting,
$$T(^{\circ}C)=\frac{5}{9}\times(400-32)$$
$$T(^{\circ}C)=\frac{5}{9}\times(368)$$
$$T(^{\circ}C)=204^{\circ}C$$
