a) What are the advantages of a worm set reducer over a simple set of spur gears? What are the disadvantages? b) What is the difference between a "single start" and a "double start" worm? Calculate the gear ratio you would have achieved if you were given a double start worm instead of a single start worm, or vice versa. Describe the different options for "worm gear enveloping"? d) How does the power transmission efficiency of a worm set reducer compared to a spur gear set?