EXPLANATION
Let's see the facts:
 Number of panes of glass = 9
 Cost = $25.65
 
 Break = 4 panes 
 Let's call x to the cost of each pane:
 9x = 25.65
Dividing both sides by 9:
 x= 25.65/9
Simplifying:
 x= 2.85
Now, multiplying the cost of each pane by the number of the others 4 panes:
 2.85*4 = 11.4
The cost is $11.4