How many 3-liter balloons could the 12-L helium tank pressurized to 160 atm fill? Keep in mind that an "exhausted" helium tank is not empty. In other words, once the gas inside the tank reaches atmospheric pressure, it will no longer be able to fill balloons.

640 balloons

Explanation:

When filling the balloon, the pressure of helium will be equal to the atmospheric pressure (the system must be in equilibrium with the surroundings). So, by Boyle's law we can calculate how many liters are necessary for the pressure of the tank:

P1*V1 = P2*V2

P1 is the pressure of the tank, V1 is the volume of the gas leaving the tank, P2 is the pressure in the balloon, and V2 the volume of the balloon.

160*V1 = 1*3

V1 = 0.01875 L of helium for each balloon

So, if there is 12 L in the tank, it would be possible to fill:

12/0.01875 = 640 balloons.