@strawberry pie,
The math formula for converting between centigrade and fahrenheit is really rather simple. Centigrade, freezing is zero and boiling is 100. On the fahrenheit scale, freezing is 32 degrees, and boiling is 212 degrees. So to convert from F to C, you subtract 32 from the F temperature, divide by 9 and multiply by 5. To covert in the other direction, you divide by 5, multiply by 9 and add 32. So, for example, 0 divided by 5 is 0, times 9 is 0, plus 32 is 32 degrees--the freezing point of water in the fahrenheit scale. For the boiling point of water, 100 divided by 5 is 20, time 9 is 180, plus 32 is 212--the boiling point of water in the fahrenheit scale.
So, for your example of 102 degrees F, that's 102-32=70, divided by 9=7 and 7/9, times 5=38 and 8/9, or 39 degrees--as close as makes no difference.