Question 948289
{{{f(x)=4-5x}}}
{{{f(x+h)=4-5(x+h)=4-5x-5h}}}
{{{f(x+h)-f(x)=4-5x-5h-4+5x=-5h}}}
{{{(f(x+h)-f(x))/h=(-5h)/h=-5}}}