7) 52h because that's how you'd find the distance traveled if there was a number instead of a variable.(d=st)
8)525+3w because you have to add his original total to the amount of cds he will get and if he gets 3 every week that's 3w and then you add them to get the new total.
If it was one year it would be 2200 and you just keep adding 200 for each year.
Given:
The geometric sequence is:

1 -4
2 20
3 -100
To find:
The explicit formula and list any restrictions to the domain.
Solution:
The explicit formula of a geometric sequence is:
...(i)
Where, a is the first term, r is the common ratio and
.
In the given sequence the first term is -4 and the second term is 20, so the common ratio is:



Putting
in (i), we get
where 
Therefore, the correct option is B.
Cot x = cos x / sin x = 0.85 / 0.52 = 1.6346