Hello! :)

Use the kinematic equation below to solve for the height of the building:

Where:
d = distance, or height of the building (m)
a = acceleration due to gravity (9.8 m/s²)
t = time (seconds)
Plug in the given values into the equation:

Well, one is more effeciant than the other. I think it would run on less gass.
I think Is b the first question