Let a = speed of the plane A, and b = speed of plane B. (Assume that the net effect of the wind is negligible.) From the first sentence, the distance between A and B after each travels for 1 hour is a + b miles. From the second sentence, after 45 minutes, or 0.75 hour, the distance between A and B is 200 miles. Plane a has traveled 0.75a, while plane B has traveled 0.75b. Hence a + b = 0.75a + 0.75b +200 ==> 0.25(a + b) = 200. ==> a + b = 800. Therefore planes A and B are 800 miles apart now.
You should always count the numbers you used to make sure the total matched the total number of data. In this case, there are 20 numbers, and the total is also 20.</span>
