Re: It's a little ironic that you and the test writer used a fractional coefficient. n/t
By fractional coefficient, do you mean '9/5'? There can be no other choice. I don't understand what you mean by 'ironic'.
Between the freezing point and boiling point there are 100 Centigrade degrees or 180 Fahrenheit degrees. The Centigrade degree has to be 180/100 or 9/5 of a Fahrenheit degree, or a little less than twice as big. I could have written that as a decimal, '1.8', but I would still get the same answers out of the formula: F = (9/5)C + 32.
IF you solve the equation for C, you get C = 5/9(F-32). Once you know the boiling and freezing points in both systems, that 9 and 5 have to show up somewhere.