If you have 7 sets of numbers
<br />
\left (4,4,3,3 \right )=A
\left (NA,NA,4,4 \right )=B
\left (4,3,4,2 \right )=C
\left (4,4,4,5 \right )=D
<br />
\left (3,3,4,4 \right )=E
\left (2,4,3,3 \right )=F
\left ( 4,4,4,4 \right )=G

If we find the mean each set, then find the mean of all the sets to that:
(S=total # of sets M=mean)

\frac{A+B+...+G}{S}=M

How would we account for the two missing values in B?
Would it be wrong to only use the two values?