Express Jenny's age in terms of a if jenny is three years less than half of Anne's age Express Fraz's age in terms of a if Fraz is twice the sum of Anne's age and 7

Sara goes on a slingshot ride in an amusement park. she is strapped into a spherical ball that has a radius 3*10^2 of centimeters. what is the volume of air in the spherical ball? use this formula: volume of a sphere=4/3pi,r^3 , where r is the sphere’s radius.