Question 295655
First compute f(a+h) and f(a). So {{{f(a+h)=4(a+h)+5=4a+4h+5}}} and {{{f(a)=4a+5}}}



This means that {{{f(a+h)-f(a)=(4a+4h+5)-(4a+5)=4a+4h+5-4a-5=4h}}}