Change your units to the one that works for this equation, which I am guessing is in meters for a 3 m wing length.
Apply a pressure load to the surface. Click on Magnitude in the Details and use the button to pull down to Function.
Type in the formula. In the graph controls, set the Range Maximum. The number of segments controls how many line segments it will use.
If you change your units to mm after you have done this and solve, you will get the wrong pressure. The equation doesn't update when you change units. You must solve in meters if that is what the equation represents. The safe way to operate is to click on Analysis Settings and set the Solver Units to Manual, then it will always solve in meters even if you switch to mm in Mechanical for meshing or other needs and leave it there.