The answer is C. 75. Hope this helps.
Step 1: Assign variable for the unknown that you need to find.

Step 2: List the given details
Distance between you and your friend is 12 miles. It means the total distance traveled by you by walk and your friend using bicycle when both travel towards each other to meet in 't' hours
Equation 1:

Your Walking rate and your friends Cycling rate is given below:

Step 3: Set up an equation using the relationship between distance, time and rate.


Substituting the above in equation 1

Distance traveled by you by walking from home and distance travelled by your friend in cycle in 0.8 hours is given below:

Answer:
a)
And rounded up we have that n=4906
b) For this case since we don't have prior info we need to use as estimatro for the proportion 
And rounded up we have that n=6724
Step-by-step explanation:
We need to remember that the confidence interval for the true proportion is given by :
Part a
The estimated proportion for this case is 
Our interval is at 90% of confidence, and the significance level is given by
and
. The critical values for this case are:
The margin of error for the proportion interval is given by this formula:
(a)
The margin of error desired is given
and we are interested in order to find the value of n, if we solve n from equation (a) we got:
(b)
Replacing we got:
And rounded up we have that n=4906
Part b
For this case since we don't have prior info we need to use as estimatro for the proportion 
And rounded up we have that n=6724
B is the answer i had this on my test the other day
Yes because all equilateral triangles have equal angles and side lengths so they are all similar. hope i helped -J