Bhaskara II Acharya/Lilavati/Chapter V

Bhaskara II Acharya: Lilavati Chapter $\text {V}$: Progressions

Problem $124$

In an expedition to seize his enemy's elephants, a king marched $2$ yojanas on the first day.

Say, intelligent calculator, with what increasing rate of daily march did he proceed, since he reached his foe's city, a distance of $80$ yojanas, in a week?