Considering balloon to be an spherical object
Volume of sphere = , where r is the radius of sphere.
After 19 minutes ,If radius of balloon changes from r to R, the Volume changes from V to V'.
V'= ,
As given,rate at which the air leaked out of the balloon (in liters of air per minute) was half of the rate at which Vavilen inflated the balloon.
Also,
Now, again the radius changes from R to r.So, Volume changes from V' to Back to V.
Time taken by the balloon to deflate = 38 minutes
But there is no relation between time and volume of Balloon.
So, we can't predict at which rate balloon is deflating or inflating.Apart from the statement given in Question: