#### Answer

$d(P, R)=12$

#### Work Step by Step

RECALL:
The distance between the points P and R on a number line, whose coordinates are p and r, respectively, is given by the formula:
$d(P, R) = |p-r| \text{ or } d(P, R) = |r-p|$
Use the formula above to obtain:
$d(P, R)
\\=|8-(-4)|
\\=|8+4|
\\=|12|
\\=12$