C.
Although this is not the exact answer the circumference formula is 2(pi)r. Which is far more than the other two options.
I believe this is how you solve it
This is from another website. <span>Simple interest is money you can earn by initially investing some money (the principal). A percentage (the interest) of the principal is added to the principal, making your initial investment grow!</span>
Basically the question is asking YOU when you hear “system of equations” what do you think about it - what do you already know about system of equations. Basically. Btw enjoy this picture.