question_answer

If the mean of 6 observations\[\mathbf{x},\mathbf{x}+\mathbf{3},\mathbf{x}+\mathbf{6},\mathbf{x}+\mathbf{9},\mathbf{x}+\mathbf{12},\mathbf{x}+\mathbf{15}\] is 18, find the mean of first 4 observations.

A) 25                      

B)       18

C) 15             

D)     36

E) None of these