Emily sees a ship traveling at a constant speed along a straight section of a river. She walks parallel to the riverbank at a uniform rate faster than the ship. She counts $210$ equal steps walking from the back of the ship to the front. Walking in the opposite direction, she counts $42$ steps of the same size from the front of the ship to the back. In terms of Emily\textquotesingle s equal steps, what is the length of the ship? (2021 Fall AMC 10A Problems, Question \#11) 
选项为:A:$$70$$  B:$$84$$  C:$$98$$  D:$$105$$  E:$$126$$  请回答其中一个选项.