The list type doesn't have operator minus defined on it
To solve the first problem, just make the list items be floats or whatever: Skip the quotes
To solve the second problem, you can iterate over the lists in a variety of ways.
f you understand list comprehension, and the zip function, you could do something like zip the two lists into tuples then subtract tuple at index 1 from the tuple at index 0. I'm not going to give you the answer: Look up list comprehension and the built in function zip However, I will note that I solved your problem with a single short line of code.
Another way to do it would be to do something like
result = 
for index in range(len(l1):
# do something useful with l1[index], l2[index] and result
What happens in either case if the lists are not the same length? What should you do about that possibility?