Write an equivalent expression in relational algebra for the following sql query?
select p. name, c. name
from professor p, course c, taught t
where p. id = t. profid and t. semester = 's2002'
and t. crscode = c. crscode

Pp 4.1 design and implement a class called sphere that contains instance data that represents the sphere’s diameter. define the sphere constructor to accept and initialize the diameter and include getter and setter methods for the diameter. include methods that calculate and return the volume and surface area of the sphere (see pp 3.5 for the formulas). include a tostring method that returns a one-line description of the sphere. create a driver class called multisphere, whose main method instantiates and updates several sphere objects.