The only "complication" here is that the directions are given in two different forms. "320 degrees from due north" I assume is measured clockwise (as on a compass) and so the angle between the two directions is 320- (90+ 87)= 143 degrees. After one hour, the first airplane will have flown 200 km and the second 150. So you have a triangle with two sides of length 200 km and 150 km and angle between them 143 degrees. You can use the 'cosine law" to find the third side of the triangle, the straight line distance between the two airplanes.