problem with weights

part1 (easy) given a standard balance scale, and a weight of unkown mass between 1 -121 grams; find the fewest number of fixed weight values to determine the mass, and thier values.
part2 (hard) after solving part 1, you must now determine the mass of the obect with the fewest number of weighings, given only the following possible operations.
a) add a wieght to one side or the other.
b) remove a weight from one side or the other.
c) change a weight from one side to the other.
you are allowed to start with any weight configuration to help reduce the number of operations nessicary. what's the best, worst case senario?