A group of 10 items has arithmatic mean 6. If the arithmatic mean of 4 of these remaining item is 7.5 then the mean of the remaining item is

Question

$\begin {array} {1 1} (A)\;6.5 & \quad (B)\;5.5 \\ (C)\;4.5 & \quad (D)\;5.0 \end {array}$