Answer:
A. The balloons will increase to twice their original volume.
Explanation:
Boyle's law states that the pressure exerted on a gas is inversely proportional to the volume occupied by the gas at constant temperature. That is:
P ∝ 1/V
P = k/V
PV = k (constant)
P = pressure, V = volume.

Let the initial pressure of the balloon be P, i.e.
, initial volume be V, i.e.
. The pressure is then halved, i.e.

Therefore the balloon volume will increase to twice their original volume.
Easy peasy! All we need to do is plug this formula into our calculator:
-log(M)
So, we'd plug in -log(.2), which is 0.7 :)