- The standard formula for temperature conversion from Celsius (°C) to Fahrenheit (°F) is °F = (°C × 9/5) + 32. - Since 9/5 is equal to 1.8, the formula can be written as °F = (1.8 × °C) + 32. - The given formula is °F = X + (1.8 × °C). - Comparing the standard formula with the given formula, we can see that X must be 32.