If the simple interest on $4000 for 9 years is $1800, then what is the interest rate.

5%

Step-by-step explanation:

4000 * 9 * r = 1800

r = 1800/36000

r = 0.05 * 100

5%

9% or 0.09

Step-by-step explanation:

so 1800/4000 is. 45 then we do. 45/5 which is 0.09 and if u wanna double check do 4000 x 0.09 then that gives us 360 then we do 360 x 5 for 5 years that you've been investing which leaves us with 1800 which is the interest you got.