Permissible and Impermissible employment

Earning through doing class assignments and exams for people

Q: I have a question regarding one domain of modern day freelance work. People contact me through the freelancing website (where I have my profile made that mentions the subjects that I'm expert in) and ask me to do their class assignments and projects. Sometimes, they also require help on their tests and exams both online and inside the class. We decide a price with mutual consent and I get paid once the work is delivered.

Now I have a couple of questions:

1- Is this mode of earning permissible?

2- If not, then what about all the money that I have earned and spent on myself and my family till this time and this amount will turn out to be not so little as I've been working in this mode for last 2 years.

3- What about the profits and investments in the property and other traditional businesses that I have done using this money that I have earned from the above mentioned work mode?

4- What about the savings that I have in hand for the time being?