Question 465633
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Hi,
Let x and (14-x) represent the number of 60sec and 30sec commmercials respectively
Question states***
 60x + 30(14-x) = 11*60
Solving for x
      30x = 660 - 420
       30x = 240
         x = 8, the number of 60sec.  Six the number of 30sec

CHECKING our Answer***
 8*60 + 6*30 = 480 + 180 = 660sec or 11 min