In order to figure out what N is you have to isolate it by dividing by 50 on both sides as shown below:
Ok so first you will need 3 bags since 12*2 is 24 that wont be enough for the whole class so 12*3= 36 so now that we figured out how many bags we need now we have to multiply $8.00 by three the answer is $24
Solution :
Given that :
The radius of circle A = 6 cm
The radius of circle C = 4 cm
In circle A

The length of arc EF = 

= 14.653 cm
In circle C

The length of arc GH = 

= 9.769 cm
Therefore,
The length of EF is 14.653 cm
The length of GH is 9.769 cm
The length of EF is 1.5 times the length of GH
i.e. 14.653 = 1.5 x 9.769
14.653 = 14.653
Hence proved.