Answer:
-2
Step-by-step explanation:

4/5-3/7. First they need the same denominater: 4/5(7)=28/35, 3/7(5)=15/35. 28/35-15/35. Now subtract numerators: 28-15=13. So your answer H. 13/35 :)
The number of ratios from students to adults would be a/s
The relation between a and s is given to be:
a = 640s
where,
a = number of acres
s = number of square miles
We are to find the number of acres for 7.5 square miles.
This means, s = 7.5
Using the value in the formula, we get:
a = 640 x 7.5 = 4800 acres
So the answer to this question is option B