We are given the equation here :

Here 1/4 is in addition on the left side, so we will use opposite operation of addition on the right side.
Opposite operation of addition is subtraction.
So subtracting 1/4 from right side, we have:

In case of fractions addition or subtraction , we have to find the least common denominator first.
LCD for 2 and 4 is 4,

f=-15/4
Answer : The value of f is (-15)/4