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:
x=40
Step-by-step explanation:
2x+7+x-10+63=180
3x=120
x=40
Answer:
55.55% decrease
Step-by-step explanation:

In the question ,
Initial point value = 9
Final point value = 4
Change% = 
1200 = 100%
35% of 1200 = 420
1200 + 420 = 1620
There are 1620 students enrolled this year.