$By$ about how much will $f(x,y,z)=ln\sqrt[\phantom{2}]{x^2+y^2+z^2}$ change $if$ the point $P(x,y,z)$ moves from $P_0(1,4,12)$ a distance $ofds=0\mathrm{.}1$ unit $in$ the direction $of3i+6j-2k?$

The change $in$ value $is$ about $df$~~

$(Roundto$ four decimal places.$)$