Answer:
Find the explicit from for the sequence  :
:

This next question I edited a bit.  Your question just says find the four terms.  I'm assuming they meant the first four. I also changed the c to an  .
.
Find the first four terms of the sequence given by:  :
:
a) 2,1,0.-3
You might want to read that second question again because there is errors in the question or things that don't really make sense.  I made my own interpretation of the problem based on my own mathematical experience.
Step-by-step explanation:
So your first question actually says that you can find a term by taking that term's previous term and adding 4.
So more terms of the sequence starting at first term 6 is:
6,10,14,18,....
This is an arithmetic sequence.  When thinking of arithmetic sequences you should just really by thinking about equations of lines.
Let's say we have this table for (x,y):
x  |   y
----------
1      6
2    10
3     14
4     18
So we already know the slope which is the common difference of an arithmetic sequence.
We also know point slope form of a line is  where m is the slope and
 where m is the slope and  is a point on the line.  You can use any point on the line. I'm going to use the first point (1,6) with my slope=4.
 is a point on the line.  You can use any point on the line. I'm going to use the first point (1,6) with my slope=4.

 :I added 6 on both sides here.
    :I added 6 on both sides here.
 :I distribute here.
     :I distribute here.
 :This is what I get after combining like terms.
        :This is what I get after combining like terms.
So  and
 and  so you have:
 so you have:

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The first four terms of this sequence will be given by:

 so it is between choice a, c, and d.
 so it is between choice a, c, and d.

To find  replace n with 2:
 replace n with 2:




So we have to go another further the only one that has first two terms 2,1 is choice a.