We can put this word problem into an equation.
1/3x = 7
Now we just have to solve for x. To find x we need to multiply by three on both sides.
1/3x = 7
*3 *3
-------------
x = 21
So it will take 21 hours to paint one wall.
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>.
Answer:
y = -2x + 12
Step-by-step explanation:
Step 1: find the slope
y = 1/2x + 5
The equation of the line is
y = mx + c
m - slope
m = 1/2
Note : if two lines are perpendicular to the other, both lines are negative reciprocal of each other
m = -2
Step 2 : using a point slope form
y - y1 = m( x - x1)
( 2 , 5)
x1 = 2
y1 = 5
y - 2 = -2( x - 5)
y - 2 = -2x + 10
y = -2x + 10 + 2
y = -2x + 12
The equation of the line is
y = -2x + 12
I dunno the answer so I just found another answer I found in here for this question:P
Sorry- it’s useless