Subtracting Elements of a Sublist in Python 3

[pangloss3030]

Hello,

I am having an issue with subtracting sublists. With the given sublist:

first_list: [[0, 1], [2,4], [8,7]]

There is supposed to be a new list where that contains the difference of the first element from the second element in the sublist:

[-1,-2,-1]

This is the code so far:

for sub_list in data:
differences.append((int(sub_list[1]))-(int(sub_list[0])) in data)

I tried to run this with the other part of the problem to multiply the resulting list, but it fails. It seems to be not iterating. Can anyone offer some suggestions?