The number of pumps in use at both a six-pump station and a four-pump station will be determined. Give the possible values for each of the following random variables. (Enter your answers in set notation.)
(a) T= the total number of pumps in use
(b) X= the difference between the numbers in use at stations 1 and 2
(c) U= the maximum number of pumps in use at either station
(d) Z= the number of stations having exactly two pumps in use