A trolleybus of total mass Mt=15 tonnes (without any passengers) and of volume Vt=90 m³ is entering a bridge over a river. Unfortunately, the bridge is being reconstructed, and careless workers forgot to put up no entry signs. The trolleybus falls into the river. What is the maximum percentage of the trolleybus volume that can be occupied by passengers such that after the fall, the trolleybus ends up floating to the surface? Consider the density of the human body to be the same as the density of water. The trolleybus is airtight.