An object of mass m is thrown vertically upward from the surface of Earth, where the acceleration due to gravity is ga. The initial speed is va, and the object reaches a maximum height of ya. If a similar object is thrown upward with initial speed vb = 7va from the surface of Jupiter's moon Ganymede, its maximum height is yb. The acceleration due to gravity on Ganymede is gb. Express the ratio of yb to ya in terms of ga and gb.