4. Suppose that the following data represent the units of production turned out each day by three different machinists, each working on the same machine for three different days:

Machinist Machine A B C B1 15, 15, 17 19, 19, 16 16, 18, 21 B2 17, 17, 17 15, 15, 15 19, 22, 22 B3 15, 17, 16 18, 17, 16 18, 18, 18 B4 18, 20, 22 15, 16, 17 17, 17, 17 Using a 0.05 level of significance, test whether

(a) the differences among the machinists are significant,

(b) the differences among the machines are significant, and (c)

the interactions are significant.