Answer:
18 years
Step-by-step explanation:
We can apply the future value formula as below
A = P x ( 1 + r) ^ n
where A is the amount: $100
P= principal amount : $50
r=4% or 0.04
n = ??
Therefore
$100 = $50 x ( 1+ 0.04)^n
$100 = $50( 1.04)^n
1.04^n =$100/$50
1.04^n= 2
n =log 2/ log 1.04
n=0.30102999/0.0170333
n=17.67 years
=18 years