As the headwind comes at the head of the plane, therefore 50 mph headwind slows the plane down.
Thus actual speed of plane with headwind, [tex]v=550- 50=500 mph[/tex]
Now using the formula , [tex]velocity= \frac{distance}{time}[/tex]
[tex]500 mph = \frac{1250 mile}{time}[/tex]
[tex]time = \frac{1250 mil}{500 mph}[/tex]
[tex]time = 2.5 hour[/tex]
Hence plane will take time to complete the distance 1250 mile in 2.5 hours