To convert Fahrenheit to Celsius, you must first subtract 32 from the Fahrenheit value and then divide the result by 1.8 (or 5/9). This conversion can make it difficult to mentally perform in you head without the use of a calculator or conversion chart such as the one provided on this page. -74f to c = -58.88888889°C. -35f to c = -37.22222222°C. More @Wikipedia
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