Given :
Initial mass , a = 150 gm .
Half time ,
.
Final mass , x = 18.75 gm .
To Find :
The time taken to decay 18.75 gm .
Solution :
We know , time taken is given by :
Here , k is a constant given by :
Putting all given value in above equation :
We get :
Therefore , time taken is 6.94 hours .
Hence , this is the required solution .