Angle = 20° for 7 hours
Speed V = x/ 1.7 = y / 4.7
Then
x= 1.7V
y= 4.7V
z= ?
Angles are
a= 90° - 70°= 20°
b= 110°
c= 50°
Now apply rule of Sinus
Sin 20/ 4.7 = Sin 130/ z
Then
z= (Sin 130/Sin 20 )• 4.7
z= 10.53
Then answer is
Plane is at 10.53 hours , from starting point.