To convert degrees Celsius to degrees Fahrenheit, you can use the formula: F = (C × 9/5) + 32. In this case, we want to find out what 21 degrees Celsius is in Fahrenheit.
Using the formula, we can substitute 21 for C:
F = (21 × 9/5) + 32
This simplifies to:
F = (21 × 1.8) + 32
F = 37.8 + 32
F = 69.8
Therefore, 21 degrees Celsius is equal to 69.8 degrees Fahrenheit.