Let f(x)=14x+3\displaystyle {f{{\left({x}\right)}}}=\frac{{1}}{{{4}{x}+{3}}}. Expand and simplify:

f(x+h)f(x)h=\displaystyle \frac{{{f{{\left({x}+{h}\right)}}}-{f{{\left({x}\right)}}}}}{{h}}= (Enter your answer in reduced form)