Mr. Kelly was checking out his items at Dunkin Donuts, he bought three bags of coffee that cost $6.75 each. There is a sales tax of 8.75%, how much will Mr. Kelly pay in total? ​

The coverage of a base station of a telecommunication company forms a disk with a radius of (kilometers). let be the distance of a cellphone from a base station. assume that the location of cellphones in use are randomly uniformly distributed within the disk. calculate the mean and variance for the random variable.