The time (t) it will take for the train to reach to Grenoble is the quotient when the distance (d) is divided by the speed (s). That is,
t = d / s
Substituting the known values,
t = 480 km / 180 km/h
t = 2.667 h
Thus, it will take approximately 2.7 h to reach Grenoble. The answer is letter D.