The correct answer is A) 6.0. The mechanical advantage of a tackle system is determined by the number of rope parts supporting the load. In the illustration D029DG, tackle number 11 has 6 rope parts supporting the load, which gives it a mechanical advantage of 6.0. The other answer choices are incorrect because: B) 5.5 is too low for a 6-part tackle system. C) 7.0 is too high for a 6-part tackle system. D) 5.0 is the mechanical advantage for a 5-part tackle system, not a 6-part system.