I'm going to assume you meant to write fractions (because if 
are all non-negative integers, the series would clearly diverge), so that
and so on.
a. If the pattern continues as above, we would have the general term
b. Note that we can write as
The series diverges by comparison to the divergent series
700 - 175 is equal to 525 when you divide that by 35 you get 15 which is your answer.
To add the two expressions, we can write it as:
4.6x-3 + (-5.3x+9)
We can distribute the plus sign (which means just drop the parenthesis in this case):
4.6x-3-5.3x+9
Now, we can simplify by combining like terms:
-0.7x+6
