The correct formula to convert Fahrenheit to Celsius is C = F-32 x 5/9
The first step would be to replace F with 64 and the subtract 32 from F.
c = 64-32 x 5/9
C = 32 x 5/9
C = 17.8
The answers are:
Substitute 64 for F
Subtract 32 from F before multiplying