echo question
If you have a rear problem in the echo aircraft always use the formula method.
If you have a forward problem where you are asked to shift weight always use the formula. The reason is because by shifting weight you are not changing the overall weight of the aircraft. Therefore the forward cg limit remains constant and therefore it can be used in the formula.
if you have a forward problem where you are asked to add or remove weight then the overall weight of the aircraft will change. this will change the forward cg limit. We dont know how much to add or remove, so if we dont know the weight, we dont know the forward cg limit. Tackle this problem graphically.
good luck with the exam. if you do drop the exam send me a pm. if you are in melbourne happy to sit down and go through it for the cost of a beer. cheers.