The minimum and maximum values are the extreme ends of the spectrum of range for wind speed. The base wind speed must be somewhere between the 2 values. It is called the mean.
Mean = (74 + 95)/2 = 84.5
Then, you find the difference of the values to the mean: 84.5 - 74 = 10.5 95 - 84.5 = 10.5
The area of a triangle is base * height / 2, or in the case of a right triangle (like this), the legs multiplied by each oehter then halved is the area.