For this case, what we should do is use the given equation.
A = P (1 + r) ^ t
Substituting values we have:
3900 = 1100 * (1 + 0.04) ^ t
Clearing t we have:
(1.04) ^ t = (3900) / (1100)
log1.04 ((1.04) ^ t) = log1.04 ((3900) / (1100))
t = log1.04 ((3900) / (1100))
t = 32.3 years
Answer:
the time will be:
t = 32.3 years