Let $y=f(x)=x^{1 / 4}$ and $x=16$ and $\Delta x=2$
So, $\Delta y=\left(\frac{d y}{d x}\right) \Delta x$
$=\frac{1}{4}\left(x^{-3 / 4}\right) \Delta x$
at $x=16$ and $\Delta x=2$
$\Delta y=\frac{1}{4} \times \frac{1}{8} \times 2=\frac{1}{16}$
and $y=(16)^{1 / 4}=2$
So, $y+\Delta y=2+\frac{1}{16}=2.0625$