We know that
Mean =Sum of observationsNumber of observations
⇒x + x + 2 + x + 4 + x + 6 + x + 85=11
⇒5x + 205⇒x+4=11
⇒x=7
So, the first three observations are x, x + 2 and x + 4.
x=7
x+2=7+2=9
x+4=7+4=11
Hence, the required mean of first three observations is
⇒7 + 9 + 113=273=9.