Divide 3 1/2 by 7= 1/2 a cup per person
After each hour 60% ( or 0.60) of the drug will be present.
The equation is A = 100(0.6)^t where t = time in hours. (answer)
Let us consider 48 as 100%
so,
48------------->100
x -------------->75
therefore,
100*x=48*75
x=(48*75)/100
x=36
