Hey there!!
The question states that a sum is invested which is $3000 and hence, this would be counted as the principle amount or the principle sum.
The term given is 3 years, which gives us the idea that this interest is being counted or being active for 3 years.
She ( Diana ) earned the sum $450 at the end of three years. This means, the simple interest is $450.
Never get confused with the principle amount, principle sum and interest.
<u><em>Principle amount = Principle sum + The interest. </em></u>
Formula given :
I = prt
'p' is denoted as the principle sum, r is the rate and the t is the term or the number of years.
Now, plugging in all the values :
... <em>450 = 3000×r×3 </em>
... <em>450 = 9000×r </em>
... <em>r = 450 / 9000</em>
... <em>r = 0.05 </em>
... <em>r = 5% </em>
As we need the answer in the decimal form, the answer would be <em><u>0.05</u></em>
Hope my answer helps!!<em> </em>
