To solve this, we first need to find a common denominator for all fractions involved.

The common denominator for 1/20, 1/4, 1/25, and 4/5 is 100.

Now, we convert each fraction to have a denominator of 100:

1/20 = 5/100
1/4 = 25/100
1/25 = 4/100
3 4/5 = 19/5 = 380/100

Now the equation becomes:

(5/100 - 25/100) /25 = (4/100 - 380/100) = -376/100

Simplifying the result, we get -376/100 = -94/25

Therefore, the answer is -94/25 or -3 19/25.