Rooftop Drone | PuzzledQuant

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Easy

Combinatorics

A delivery drone sits on a street corner of a city grid at coordinates $(0,0,0)$ . Its drop-off point is on a rooftop at $(6,4,2)$ : 6 blocks east, 4 blocks north and 2 levels up. At every step the drone moves exactly one unit in a single direction: east, north or up. It never moves west, south or down.

How many different routes can the drone take from $(0,0,0)$ to $(6,4,2)$ ?

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