Answer:
A) 
B)
C) d=200-7t
D) t=28.57s
Step-by-step explanation:
A) in order to solve this part of the problem, we must remember that velocity is the ratio between a displacement and the time it takes for a body to go from one point to the other. So we can write it like this:

when solvin for the distance x, we get the formula to be:

We can use this to write the expression they are asking us for, so we get:

B) the procedure for part b is the same as the procedure for par A with the difference that Carolyn's speed is different. So by using the same formula with Carolyn's speed we get:

C)
In order to find the distance between Ian and Carolyn, we subtract the distances found on the previous two questions from the 200ft, so we get:

we can further substitute the d's with the equations we found on the previos two parts of the problem, so we get:

which simplififfes to the following:
d=200-7t
D) we can figure the seconds out by substituing the distance for 0 and solving for t, so we get:
0=200-7t
which can be solved for t, lke this:
-7t=-200
