Respuesta :

He has 2 jobs paying different rates.  

At $15/hr for 8 hours, he earns $120.
At $18/hr for 4 hours, he earns $72.

Summing these up:  $120 + $72 = $192

Dividing by the total # of hours worked (12),

$192
---------  = $16/hr   (average rate)
 12 hr