The significant figures correspond to the number of digits that a number contains, but we must take into account that the zeros at the beginning and end of the number are not counted, only the zeros are counted if they are in an intermediate position.
For example, for the number 0.500, there will only be one significant figure that corresponds to the number 5.
For the number 0.40001 we will have 5 significant figures, since the intervening zeros must be counted.
For question 1) we will have:
Answer: We have in 956, three significant figures