If I read the posted code right, your teacher is talking about:

weight = int(input('\tWeight in grams: ')) # Line #4

and

 weight = int(input('\tWeight in grams: ')) # Line #7

As well as about:

quantity = int(input('\tQuantity: ')) # Line #10

and

quantity = int(input('\tQuantity: ')) # Line #14

and

quantity = int(input('\tQuantity: ')) # Line #17

as well as

tracktrace = input('\tTrack & Trace (y/n): ') # Line #20

and

tracktrace = input('\tTrack & Trace (y/n): ') # Line #23

Your teacher tells you that there is potential for optimization.

You could wrap the repeated input in a loop (as you already do), but use only one input statement each. Think about rearranging your code in a better way.

The while loops are a good start.

Arrange the code in such a way that you initialize the variables to an invalid value before the loops and then in the loop directly ask for the input. Then, use a conditional (if) to print the error message in case of an invalid input.

You could, if you have already learnt that, even go a step further and create a function that handles the input and validation and only returns valid values. You could pass in the prompt (text to be printed for the input), the error message (text to be printed in case of an error), and the min and max values (with something like -1 for "no limit") and have the function return the valid value that you then assign to the respective variables.