A survey of

companies was conducted. There are

companies that have a Facebook presence. There are

companies that have a Twitter presence. There are

companies that have both a Facebook presence and a Twitter presence.

For clarification, there are

companies that have a Facebook presence $($and this tally includes companies that have a Twitter presence and those that don't have a Twitter presence.$)$

$($a$)$ How many companies have a Facebook presence or a Twitter presence?

$($b$)$ How many companies have neither a Facebook presence nor a Twitter presence?

$($c$)$ How many companies have a Facebook presence and do not have a Twitter presence?