Space invaders land on earth. On the invaders' temperature scale, the ice point is at 21I (I = invader), and the steam point is at 153I.

Space invaders land on earth. On the invaders' temperature scale, the ice point is at 21°I (I = invader), and the steam point is at 153°I. The invaders' thermometer shows the temperature on earth to be 51°I. Using logic similar to that in Example 1 in the text, what would this temperature be on the Celsius scale?