Let us say that s is the speed of the plane and x is the speed of the headwind so that:
s – x = (320 / 2) = 160
s + x = (320 / 1.6) = 200
So we got two equations:
s – x = 160
s + x = 200
Adding the two equations:
2s = 360
s = 180 mph (speed of plane)
So x is:
x = 180 – 160
x = 20 mph (headwind)