Find an equation for the nth term of the arithmetic sequence. 9, 11, 13, 15

An arithmetic sequence has the form as
 
where  = n-th term,
  = first term,
d = common difference

We can see that 11 – 9 = 13 – 11 = 15 – 13 = 2. So the common difference is d = 2.
The first term is . So the n-th term of the sequence is

So the answer is 

31/6= 19/6 19/6 *1/7=19/42

The answer is 4 points