You know that the sum of a and b is 24, because the average is the sum of the numbers divided by the amount of numbers added together, and 12*2 is 24. Add 3 to 24 so you have 27, and then divide that by 3 because there are now 3 numbers in the set. The average of a, b, and c is 9.
It would be in passive voice. For active voice, it would be something along the lines of, "The FBI opened the email."
The first step in the five step process for problem-solving is to recognize that the problem exists
I don't see anything wrong with traveling
B. it is an English sonnet