Which formula correctly shows how to calculat the time taken, given the average velocity and the displacement

An object moves from the position +34m to the position -15m in 15 seconds. what is it's total displacement? what is it's average velocity?

The ratio of lift to drag l/d for a wing or airfoil is an important aerodynamic parameter, indeed, it is a direct measure of the aerodynamic efficiency of the wing. if a wing is pitched through a range of angle of attack, l/d first increases, then goes through a maximum, and then decreases. consider an infinite wing with an naca 2412 airfoil. estimate the maximum value of l/d. assume that the reynolds number is 9x10^6.

The movement of electrons between atoms is called an