An exceptional standing jump would raise a person 0.80 m off the ground. To do this, what force must

An exceptional standing jump would raise a
person 0.80 m off the ground. To do this, what force must a 68 kg person exert
against the ground? Assume the person crouches a distance of 0.20m prior to
jumping, and thus the upward force has this distance to act over before he
leaves the ground.