#### Answer

r = 2.19

#### Work Step by Step

We first use trigonometry to find the missing sides:
$ AC = 12sin(60) = 10.4 $
$ BC = 12 cos(60) = 6$
We use the known formula to obtain:
$r = \frac{ab}{a+b+c} \\ r = \frac{6(10.4)}{6+10.4+12} \\ r = 2.19$