Elliot borrows $900 to buy an appliance at a yearly simple interest rate. He takes 3 years to pay off the loan and interest. He pays $135 in interest. What is the interest rate?

He pays $135 for 3 years. So that’s $45/year. Considering 900 is your 100%, how many percents are represented by $45 in 900?

1)
You can see that 900 = 9x100.
So you can divide 900 by 9 to get 100.
That means you can also divide 45 by 9 (it’s proportional)
You have 45 for 900, you divide by 9 so you get 5 for 100 -> 5%

Or 2)
(Photo)
It’s a cross-multiplication :
(45 x 100)/900 = 5%
So the interest rate is 5%.

(Sorry if it’s confusing, English isn’t my first language..)