(2) -40° Explanation: If C is the temperature in Celsius and F is the temperature in Fahrenheit then, C/S = (F-32)/9. They are equal at -40° (minus 40 degrees), because if we convert the readings of Celsius and Fahrenheit, we will have: Celsius to Fahrenheit (-40°C x 9/5) +32 = -72 + 32 = -40°F. Fahrenheit to Celsius (-40°F - 32°) x 5/9 = (-72) x 5/9 = -40°C.