Answer:
Correct choice is B
Step-by-step explanation:
In step 4 were proved that 
By definition, similar triangles have proportional lengths of corresponding sides. To the side AB corresponds side ED, to the side AC corresponds side DC and to the side BC corresponds side EC. Thus,

600 + 9.5x (less than or equal to) 900
600 fixed amount
9.5 is the variable changing amount and differs among number of students taken
Here you go.................
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