Question

Maria earned $126 in simple interest from her savings account. If she invested $450 for 7 years what was the interest rate?

Answer 1

The answer is B. You didn't mention compounding, so I have to assume that this is simple interest. The formula for simple interest is 
Interest = principal * interest rate expressed as a decimal * time in years. 
$126 = $450 * X * 7. Now multiply $450 * 7 years = $3,150 
$126 = 3,150X 

What has been done to the X? It was multiplied by $3,150. What is the opposite of multiplication? It is division. Remember that whatever we do to one side of the equal sign we must also do to the other side of the equal sign. 

$126 = $3,150X 
-------____---------- 
$3,150__$3,150 

Any number over itself = 1. Now we have 
.04 = X 

To change a decimal to a percent move the decimal place two places to the right and add a percent sign. 
.04 = 4$. The answer is B