Graphing a Line
y = -1/6 + 1

1 is where the interception is

so star from one and go down 1 over 6 and repeat

How do you want me to answer this question, tell you how to graph the line.

Step-by-step explanation:

Well, start with your first coordinate (0,1) then use a -x=y line to move up and 1 backwards into the 2nd quadrant.

Rather than use that formula, look at the attachment and use the 4th equation.

Ending Amount = Beginning Amount / 2^n
where "n" is the number of half-lives.  "n" = elapsed time / half-life
(Is 934 the beginning amount? Let's say it is.)

for 40 years, n=40/30 = 1.3333333...
Ending Amount = 934 / 2^1.3333333...
Ending Amount = 934 / 2.5198420998
Ending Amount = 370.66 grams

for 100 years, n=100/30 = 3.333333 ...
Ending Amount = 934 / 2^ 3.333333 ...
Ending Amount = 934 / 10.0793683992
Ending Amount = 92.66 grams

Source:
http://www.1728.org/halflife.htm