Write the form $of$ the partial fraction decomposition $of$ each rational expression. $Do$ not solve for the constants.

$(a)\frac{27}{x^2-4x}$

$(b)\frac{7x^2+6}{(x-4{)}^3}$

$(c)\frac{3x-6}{x^3+13x}$

$(d)\frac{7x-5}{x(x^2+1{)}^2}$