The correct formula is C = (5/9)(F-32). If we substitute 68 for F, since that is the temp you are given, we have

C = (5/9) (68-32)

C = (5/9) 36

C= 180/9

C = 20 degrees

The correct answer for this is B -- the temperature is expressed as 20 degrees Celsius.

The formula for this conversion is

Tc = (Tf-32)/(9/5) where Tc is the temperature in Celsius and Tf is the temperature in Fahrenheit.  This can also be expressed as (Tf-32)/1.8

When we do the math based on this conversion formula, we subtract 32 from 68.  This gives us 36.  We then divide 36 by 1.8 and this gives us 20.

Therefore, the temperature that is expressed as 68 degrees Fahrenheit is also expressed as 20 degrees Celsius.