6. David has 56 baseball cards of which he sells 3 cards per week. Write an equation representing the number of cards n he has left at the end of any
given week w.

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.