In this question we have to find the effect of doubling principal, rate or time .
First we have to check the formula which is

As we see that interest is the product of principal, rate and time. So if any of these three doubles, that is if any of these three is twice of the original value, the interest gets doubled.
SO the correct option is C.
The distance formula is derived from the Pythagorean Theorem because the length of one leg of the triangle will always be the difference of the x<span>-coordinates, and the length of the other leg will always be the difference in the </span>y<span>-coordinates</span>