Answer:
   -390 mph
Step-by-step explanation:
Let a and b represent, respectively, the distances of A and B from the airport. The distance d between the planes is then given by the Pythagorean theorem as ...
   d² = a² + b²
Differentiating with respect to time, we have ...
   2d·d' = 2a·a' +2b·b'
Solving for d', we get ...
   d' = (a/d)a' +(b/d)b'
The value of d at the time of interest is ...
   d = √(a² +b²) = √(30² +40²) = √2500 = 50
Then the rate of change of separation is ...
   d' = (30/50)(-250 mph) +(40/50)(-300 mph) = (-150 -240) mph
   d' = -390 mph
The distance between planes is decreasing at 390 miles per hour.
 
        
             
        
        
        
Well. No. Because it’s supposed to be 0.122222222...
        
             
        
        
        
Assuming you made an error typing the question out, and the formula should say 30g, as it's $30 a round:

