import math


def calculate_delta_t(initial, final, speed):
    """ Return estimated time from initial to final, given a speed

    inputs:
    - initial: 2D point defining the initial position
    - final:   2D point defining the final position
    - speed:   speed used to calculate delta_t
    """
    delta_x = final[0] - initial[0]
    delta_y = final[1] - initial[1]
    distance = math.sqrt(delta_x * delta_x + delta_y * delta_y)
    return distance / speed