What does x represent

Acircle has a circumference of 28.36 units what is the diameter of the circle

Gabrielle's age is two times mikhail's age. the sum of their ages is 84. what is mikhail's age?

Pleting the square f the given find the x-intercepts of the parabola with vertex (-5,13) and y-intercept (0, 12). write your answer in this form: (14,.99). if necessary, round to the nearest hundredth. *- h enter the correct answer, de verter, and ametry 00000 done doo