First we define the variable to be used:
x: half-life time period
The equation for this problem can be modeled as:
y = A * (b) ^ x
Where,
A: initial amount
b: decrease rate.
For example:
if there are 100 atoms, after one half-life time period, 50 atoms remain:
y = 100 * (0.50) ^ x
after one half-life time period (x = 1):
y = 100 * (0.50) ^ 1
y = 50
The equation that models the problem is:
y = 16 * (0.50) ^ x
The table is:
1 8
2 4
3 2
4 1
5 0.5
The answer is 42^3 from your question
Answer:
c. In 2 seconds, the commuter train travels 120 feet.
Step-by-step explanation:
Given
The attached graph
Required
What does x-coordinate of 2 represents
Represent this coordinate with (x,y)
From the graph:
when 
Note that:
x = time and y = distance
So:

Which means:
At 2 seconds, the train has travelled a distance of 120ft
<em>From the list of options, (c) is correct</em>