It’s 21 it technically just means your increasing the 15 by 50 percent
A formula is recursive if it expresses the term
in terms of the previous one(s) 
In this case, every term is 7 more than the previous one, so the formula for
will only involve
:

In fact, this formula is simply saying: for every index
, the term with that index is 7 more than the term before.
Also, we have to specify the starting point (otherwise we would go backwards indefinitely), so the complete recursive formula is

which means: start with 2 and generate every other term by adding 7 to the previous one.
Answer:
Ah yes, one of my favorite topics.
Step 1: Which ever fraction comes first, you will solve it first. For this question, focus on doing
first. Afterwards, do 
Step 2: First one equals to 1.125. Next, find the LCD (lowest common dominator, which is 10). 
Step 3: 1.125+3/10
12.9 i think, not sure. try it though