You put $400 in an account. The account earns $18 simple interest in nine months. What is the annual interest rate

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%