Question 1021849
For sufficiently small enough h, f'(x) is very close to {{{(f(x+h) - f(x))/h}}}

==> hf'(x) is very close to f(x+h)-f(x)

==> 0.8*f'(89) is very close to f(89.8) - f(89).

Now f'(x) = {{{85+19/x}}} if f(x) = {{{85x+19lnx}}}

This means the difference is approximately equal to hf'(x) = 0.8*(85+19/89) = {{{highlight(68.17)}}}.