Explanation
Correct answer: 7.
When an equation is of the form , where , , and are constants, the value of reaches its minimum when . Since the given equation is of the form , it follows that , , and . Therefore, the value of reaches its minimum when , or .
Desmos solution:
Note: The regression finds x=7 where the derivative is zero, so the quadratic reaches its minimum there.
Enter in Desmos:
Reviewed and rewritten by CookSAT