If it is not a decimal operation, let the distance be d, the plane speed be v, the wind speed be u, the windless time be 2d/v, and the windless time be (v+u) divided by d plus (v-u) divided by 2dv/(the square of v -u), and the numerator and denominator be divided by v at the same time. When there is no wind, we can see that the molecules are the same and the denominator is less than.