You are standing across the street from a tall building when the top of the building (h = 80 m) is hit by lightning and a brick is knocked loose. You see the lightning strike and immediately see that the brick will fall to hit a person standing at the base of the building. You then run toward the person and push him out of the path of the brick, the instant before the brick reaches him. If you are initially 25 m from the building, how fast do you have to run?