Ruling on a man teaching girls without any barrier

What is the ruling on professional pursuit of football (soccer)?

He works in a video game store and is asking about his income

He works in a mixed environment and is worried about his fast

Is it permissible for a woman to work selling products over the phone?

Is it permissible to delay payment of salaries to employees?

He got his university certificate through an intermediary and got a job with it. What should he do?

Is it permissible for her to pray in front of employees at work?

Working for a company that sells gold on credit

Writing a letter stating salary for someone who will use it to get a riba-based loan