Answer: simple interest rate is 19%
Step-by-step explanation:
The formula for determining simple interest is expressed as
I = PRT/100
Where
I represents interest paid on the amount invested.
P represents the principal or amount invested.
R represents interest rate
T represents the duration of the investment in years.
From the information given,
P = 90000
I = 400000 - 90000 = $310000
T = 18 years
Therefore,
310000 = (90000 × R × 18)/100
310000 = 16200R
R = 310000/16200
R = 19%