I believe you are referring to the half-life formula, which is used to calculate the half-life (when the substance drops to half of its original amount) of radioactive substances. The equation is as follows:

<em>A</em> is the remaining amount
<em>P</em> is the initial amount
<em>t</em> is the time that has passed
<em>h</em> is the half-life of the substance
When plugging values into the equation, make sure that <em>t </em>and <em>h </em>are both measured in the same unit (e.g. <em>t </em>days and <em>h </em>days), as well as <em>A </em>and <em>P</em>.
Step-by-step explanation:
As
- The graph of the function passes through the point (2,1), and
- y increases by 4 when x increases by 1.
so
x y
2 1
3 5
4 9
5 13
6 17
and so on
From the table:




As the slope-intercept form of the line is

putting m=4 and any point, let say (2, 1) to find y-intercept 'b'.




So putting
and
in the slope-intercept form of the line


Therefore, the equation for the linear function will be:

I would go with -15 that’s what I came up with
There would be an open circle on positive 12 with the arrow moving to the right.