28 tries. The ratio is 5:7, so once you multiply 5 by 4 to get 20, you do the same to 7 to get 28.
Given:
The given arithmetic sequence is:

To find:
The recursive formula of the given arithmetic sequence.
Solution:
We have,

Here, the first term is -3. So,
.
The common difference is:



The recursive formula of an arithmetic sequence is:

Where, d is the common difference.
Putting
, we get

Therefore, the recursive formula of the given arithmetic sequence is
, where
.
You out 1 in for A and 12 in for C 4(1)(12) = 48