Considering the formula 1⁄w = 1⁄x + 1⁄y + 1⁄z, then if x = 5, y = 10, and z = 15, the value of 1⁄w is

• A. 11⁄20
• B. 11⁄30
• C. 30⁄11
• D. 20⁄11