The formula $$C = \frac{5}{9}(F - 32)$$ expresses the relationship between Fahrenheit temperature, $F$, and Celsius temperature, $C$. Use the formula to convert the given Fahrenheit temperature to its equivalent temperature in the Celsius scale.
(Note: Do not forget to include the units: For $100^\circ C$ type, 100 degC .)

$21^\circ F =$