1. To Calculate the resultant speed of the plane, you need to find the speed of the air, add it to the plane speed, then find the resultant using trigonometry.
The velocity of the plane:
east=400 knots
The velocity of the air
50knots north east = 50/√2 north + 50/√2 east
The resultant speed would be:
total speed^2= east^2 + north^2
total speed= √(400+50/√2)^2 + (50/√2)^2
total speed= √(189534.254 + 1250)
total speed= 436.8 knots
2. To count the direction of the plane, you need to find the total speed of x(east/west) and y(north/south) axis separately then use tan formula.
east speed= 400knots + 50/√2 knots= 435.35 knots
north speed= 50/√2knots= 35.35 knots
tan a= opposite/adjacent
tan a = north speed/ east speed
tan a= 35.35/ 435.35
tan a=0.0812
a= 4.6 degrees