Answer
7B9
Work Step by Step
Use Table 16.4 to find equivalent values.
$11110111001_2=\underbrace{0111}\underbrace{1011}\underbrace{1001_2}=7B9_{16}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 7\ \ \ \ \ \ \ B\ \ \ \ \ \ \ \ 9$