Answer
$1.8\space ms$
Work Step by Step
We can write the increment of the length of the day $(\Delta T)$ as follows.
$(\Delta T)= New\space length\space of\space the\space day\space-\space Previous\space length\space of\space the\space day $
$\space\space\space\space\space\space\space\space\space=86,400.0038\space s\space-\space 86,400.002\space s$
$\space\space\space\space\space\space\space\space\space =0.0018\space s$
$\space\space\space\space\space\space\space\space\space=0.0018\times\frac{10^{-3}\space s}{10^{-3}}$
$\space\space\space\space\space\space\space\space\space=\frac{0.0018\space ms}{10^{-3}}$
$\space\space\space\space\space\space\space\space\space=(\frac{0.0018\space}{10^{-3}})\times\frac{10^{3}}{10^{3}}\space ms$
$\space\space\space\space\space\space\space\space\space=1.8\space ms$
$$The\space increment\space of\space a\space day\space is\space 1.8\space ms$$
