When we say directly northeast that is equivalent to 45˚ north of east. 
 First let us determine the north and east components of the acceleration using cos and sin functions:
 North = 2.18 * sin 45 
 East = 2.18 * cos 45 
Then we set to determine the east component of the plane’s displacement by calculating using the formula:
 d = vi * t + ½ * a * t^2 
 d = 135 * 18 + ½ * 2.18 * cos 45 * 18^2 
d = 2430 + 353.16 * cos 45 = 2679.72 m
 Calculating for the north component:
 North = ½ * 2.18 * sin 45 * 18^2 
 North = 249.72 m 
  
 Hence magnitude is:
 Magnitude = sqrt (2679.72^2 + 249.72^2)
 Magnitude = 2,691. 33 m
 Calculating for angle:
 Tan θ = North ÷ East 
Tan θ = 249.72 m ÷ 2679.72 m
 θ = 5.32°
 So the plane was flying at 2,691. 33 m at 5.32°