The denominator factors as (1-x)(1+3x)
Solve the identity x≡[A(1-2x)]+[B/(1-3x)] tp get A=1/5=-B
Form 2 partial fractions.
Now divide the two fractions by long division and add them to get the coefficients required.
Don't forget the facor of 25 and the common factor 1/5 in the A and B.