Check if the Formula is Correct

Create a function that takes a string and returns True or False depending on whether or not the given formula is correct.

Examples

formula("6 * 4 = 24") ➞ True

formula("18 / 17 = 2") ➞ False

formula("") ➞ None

Notes

• You have to figure out what a is.
• Ignore the spaces.
• If the input is an empty string "", return None.
• You do not need to dynamically find the value of a (it's a constant and the same accross all tests).