The equation of motion of a missile is x = 3t, y = -4t, z = t where time 't' is in seconds and the distance is measured in kilometres.

If the position of rocket at a certain instant of time is (5, -8, 10), then what will be the height of the rocket from the ground? (Ground is considered as xy plane)

10 km

The correct answer is Option (1) → 10 km

Height will be given by 

$z=t$ (as xy plane is considered ground)

at position (5, -8, 10)

height → 10 units (km)