Arithmetic Formatter Test Fail

Tell us what’s happening:
I am failing 4 out of the 6 tests but I don’t know why my code is failing.
Also, why is my code displaying like this in the forum? I just copied and pasted but the post is displaying it in a weird format.

Your code so far

def arithmetic_arranger(problems, solve = False):

line1 = “”
line2 = “”
line3 = “”
line4 = “”

if len(problems) > 5:
return “Error: Too many problems.”

for i in problems:
first, operator, second = i.split()

if operator != '+' or operator != '-':
  return "Error: Operator must be '+' or '-'."

if not first.isdigit() or not second.isdigit():
  return "Error: Numbers must only contain digits."

if len(first) > 4 or len(second) > 4:
  return "Error: Numbers cannot be more than four digits."

if operator == '+':
  answer = int(first) + int(second)

else:
  answer = int(first) - int(second)

total_length = max(len(first), len(second)) + 2
space1 = total_length - len(first)
space2 = total_length - len(second) - len(operator) 
space4 = total_length - len(str(answer))

line1 += space1 * ' ' + first
line2 += operator + ' ' * space2 + second
line3 += "-" * total_length
line4 += space4 * ' ' + str(answer)

if i < len(problems) - 1:
  line1 += "    "
  line2 += "    "
  line3 += "    "
  line4 += "    "

arranged_problems = (line1 + ‘\n’ + line2 + ‘\n’ + line3)

if solve:
arranged_problems += ‘\n’ + line4

return arranged_problems

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.135 Safari/537.36.

Challenge: Arithmetic Formatter

Link to the challenge: