Answer
$14.4ns$
Work Step by Step
We know that
$t_{ice}=\frac{t_{ice}}{v_{ice}}$
We plug in the known values to obtain:
$t_{ice}=\frac{0.38\times 1.31}{3\times 10^8}s$
$t_{ice}=1.6593ns$
and $t_{water}=\frac{d_{water}}{v_{water}}$
We plug in the known values to obtain:
$t_{water}=\frac{2.87\times 1.33}{3\times 10^8}s$
$t_{water}=12.724ns$
Now $t_{total}=t_{ice}+t_{water}$
We plug in the known values to obtain:
$t_{total}=1.6593+12.724=14.4ns$