The answer is D. 21 because your multiplying 3 and 7
Answer: 
Step-by-step explanation:
Given
Population of dust particle doubles every 30 minutes
If the initial sample is 21 grams
The model to predict the population will be

Where t=time in hours
A day has 24 hours . So, for 2 days time is 48 hours
Population is given by
Answer:
option D. x = 1 3/5
Step-by-step explanation:
ratio and proportion
<u> 4 </u> = <u> x </u>
5 2
X multiply:
5x = 4(2)
5x = 8
x = 8 / 5
x = 1 3/5