Explanation:
°F = (°C × (9/5)) + 32, is the equation for converting degree Celsius to Fahrenheit, when °C = -78.5°C then
°F = (-78.5 × (9/5)) + 32
°F = (-78.5 × 1.8) + 32
°F = -141.3 + 32
°F = -109.3°F
Therefore, the sublimation point of dry ice at -78°C is - 109. 3° F