The square root of 51.84 is 7.2
People should conserve energy because it produces a higher quality of life. Reduced emissions result in cleaner air quality. It also helps create a healthier planet and helps sustain resources we have.

So the answer is choice D. You can check this by differentiating the right hand side and you'll get x^3 back again.
This answer can be found by using the power rule for integrals. That rule is