Answer
f=8 or f=2
Work Step by Step
$4|f-5|=12\longrightarrow$ divide each side by 4
$4|f-5|\div4=12\div4\longrightarrow$ divide
$|f-5|=3\longrightarrow$ definition of absolute value
$f-5=3$ OR $f-5=-3\longrightarrow$ add 5 to all parts
$f-5+5=3+5$ OR $f-5+5=-3+5\longrightarrow$ add
$f=8$ OR $f=2$
