5/12-3/20 use the least common multiple as the denominator

The common multiple of 12 and 20 is 60.
You've got to multiply the first one by 5 and the second by 3.
5*5= 25
This therefore becomes 25/60
The second becomes 3*3= 9
This becomes 9/60
As you're subtracting, you only subtract the numerators.
25-9= 16
Therefore, the answer is 16/60 which can be simplified to 4/10 or 2/5
Hope this helps :) 

the given function is:

f(m) = 4 (1.08)^m
part a:  
solve m when f(m) = 6.86

6.86 = 4 (1.08)^m
divide both sides by 4:
(1.08)^m = 6.86 / 4 
apply log to both sides :

m log(1.08) = log (6.86 / 4)
m = log (6.86 / 4) / log(1.08)

m = 7 months
therefore the study concluded after 7 months.
domain = [6.86, 7] 

 

now solve for f(m) when m = 0

f(m) = 4 (1.08)^0

f(m) = 4

therefore the initial length is 4 cm.

domain = [4, 0]

 

a reasonable domain is between [4, 0] to [6.86, 7]  .
part b: the y-intercept is the value of the f(m) when m = 0, so it represents the initial length of the fish at day 0. the y-intercept is:

f(m) = 4 (1.08)^0

f(m) = 4

 

part c:  
average rate of change = change in the radius / change in days
average rate of change = [ f(7) - f(3) ] / (7 - 3) = [4 (1.08)^7 - 4 (1.08)^3] / (7)
average rate of change = 1.816 / 7 
average rate of change = 0.26 cm / month

this represents the growth per month.