CPhill

A cone with the same height and radius as the cylinder will have 1/3 of the cylinder's volume.....

I think you might mean  :

√[25 * 6 ]   = 12.247 ≈ 12.25   (???)

I assume that this is:

(4/7) x=20      if so....multiply both sides by 7/4

x  =   20 * (7/4)   =  (20/4) * 7   =   5 * 7   = 35

The amount in week 30  =

.02 (2)^(15 -1) / 2 =   $ 163.84

And the accumulated amount is given by :

.02 [1 - 2^15] / [1 - 2]   = $ 655.34

"A"  is correct

The  total distance is given by :

5 [ 1 - 4^5] / [1 - 4]  =  1705 m

I realize that I made a slight mistake.... the answer should be :

2* 25.6 [ 1 - .8^9 ] / [ 1 - .8]   + 32   =  253.6 m

Sorry.......!!!!!

The sum, S_n ......is given by

S_n  = 8400 [ (1 - (1.05)^19) / (1 - 1.05) ]    =  about   $ 256,527.63

[19  =   2000 - 1982 + 1]

Vertical lines = undefined slope

Horzontal lines =  "0" slope