For each expression, write an equivalent expression that uses only addition. Do not include any spaces in your answers. Keep the terms in the same order. 20−9+8−7 and 4x−7y−5z+6

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.