Question 1237
 Sol: Let the speed of the first plane be x miles/hr and then the speed of the 2nd one is x+150 mile/hr.
 At 7pm(4 hours after the 1st plane took off) the 2nd plane flew 3hrs and was
 250 miles ahead of the 1st plane.
 So we have 3(x+150) = 4x +250,
 Or 3x + 450 = 4x + 250, So, x = 200 miles/hr and x + 150 = 350 , 
 Hence,the speed of the 2nd plane is 350 miles/hr and it travelled 
 3*350 = 1050 miles.