Answer:
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.