x B = 83+77+80+85+80+756 = 80；

(2) The median is 80;

(3)a2 = 16[(80-79)2+(80-78)2+(80-84)2+(80-8 1)2+(80-83)2+(80-75)2。

s B2 = 16[(80-83)2+(80-77)2+(80-80)2+(80-80)2+(80-75)2]≈ 18。

(4) Based on the above information, we should send A, because the performance of A is more stable when the mean and median are the same.