PLEASE HELP MATH 11. And 12.

One file clerk can file 10 folders per minute. a second file clerk can file 11 folders per minute. how many minutes would the two clerks together take to file 672 folders?

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.

The probability brenda will recieve a telemarketing call is 15%. if she gets 20 calls a day, how many can she expect to be telemarketing calls ?