Reindeers are pulling Santa Claus's sleigh along a straight line at a constant speed of $100\space km/h$. After travelling $d\space km$, the reindeers became tired. Then Santa gave them magic juice to drink. Immediately, the reindeers started running at a constant speed of $120\space km/h.$! After travelling to $2d\space km$ more in the same direction, the sleigh stopped. What is the average speed of the sleigh for the whole journey?

Your answer should be in $km/h$ unit.


NB: Submit the number only, not the unit.