What is the correct formula for average wavelength to describe surface roughness? (Where, Ra is the arithmetic mean deviation from the mean line of profile)

• A. 2π x Ra / Mean slope
• B. 2π x Ra x Mean slope
• C. 2π / Ra x Mean slope
• D. 2π / Ra / Mean slope
• E. 2π x Ra / Mean slopeb) 2π x Ra x Mean slopec) 2π / Ra x Mean sloped) 2π / Ra / Mean slope