Henry is preparing two messages: $($a$)$ a message to a long$-$time client to apologize for an error in a recent order, and $($b$)$ a message to his staff listing the final details of the upcoming company picnic.

Choose the medium for each message based on the ten levels of richness in workplace communication and explain your answer.

A

B

I

$U_{?}$

c

$x_2$

$x^2$