unsupported operand type(s) for -: 'list' and 'list' using python
You are facing the error on the line x.append((a[i] - b[i] + c[i])) due to expression a[i] - b[i] + c[i]. Let us see the how it is being calculated. Suppose I have the following data:

array([[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]])


Then the values of a, b and c are:

a
Out[20]: [[1], [4], [7]]

b
Out[21]: [[2], [5], [8]]

c 
Out[22]: [[3], [6], [9]]


Let us take i=0 and print a[0]:

Out[23]: [1]


Hence what you are calculating is [1] - [4] + [7] instead you should be calculating 1 - 4 + 7. To do this change the line with error to:

x.append((a[i][0] - b[i][0] + c[i][0]))