Answer:
t = 13.1576 years
Step-by-step explanation:
The situation can be modeled as
P = Po.(1-r)^t
Where
t is the years transcurred
Po is the initial amount
r is the rate of change
Po = 40000
r = 10% equivalent to 0.1
Now
A quarter of the original amount
(1/4)*Po = Po.(1-r)^t
(1/4) = (0.9)^t
t = 13.1576
Please, see attached picture
