The acceleration of gravity can be measured by projecting a body upward and measuring the time that it takes to pass two given points in both directions.

Show that if the time the body takes to pass a horizontal line

in both directions is

, and the time to go by a second line

in both directions is

, then, assuming that the acceleration is constant, its magnitude is

where

is the height of line

above line

.

So this is a constant acceleration problem. Also the path is parabolic. How would I deduce the above equality?