Answer:
6%
Step-by-step explanation:
Simple Interest formula:
S.I=P×R×T/100
where
S.I is simple interest
P is principle amount
R is Annual interest rate
T is time period
[usually represented as (number of months)/12]
so
$18=$400×R/100×9/12
simplify
$18=$3600R/1200
$18=$3R
so R=$18/$3
=6
Therefore,
The Annual Interest Rate is 6%
