VexGO: Robot detecting distance traveled

My students are programming their Vexgo Codebase with Eye sensor and Electromagnet to pick up the disks in the kit. They have nicely found out how to go a certain distance (ie 200mm), find a disk and return the (200mm), and they have also figured out how to travel a random distance,detect an object, and piuck it up…Here is the problem.

Problem: After picking up the object at a random distance, we do not know how to program the robot to go back the same distance to it’s starting point. Is there a way for the robot to calculate how far it has gone and return to its home spot? Thank you.