3(2a-5) = 12-7a
6a-15=12-7a
6a+7a=12+15
13a= 27
27=3c-3(6-2c)
27=3c-18+6c
27+18=3c+6c
45=9c
C=45/9
C=5
6c-8-2c=-16
6c-2c=-16+8
4c=-8
C=-8/4
C=-2
Answer:
Option B. 
Step-by-step explanation:
we know that
The frequency is equal to the number of cycles divided by the time
Remember that
1 cycle = 1 full wave to repeat itself
In this problem
From o to 12 seconds ------> there are 2 cycles
therefore
The frequency is equal to

35 if you want to count purple but 12 if your from orange
√4 / 9
√4 = 2
So the answer would be....
2 / 9
Hope this helps!