Im taking a simple introductory arithmetic math course in Uni and the professor I have is using bizarre methods to solve seemingly simple world problems. I would like to solve this problems algebraically as Im most comfortable using this method, only problem is that I have forgotten the ways to solve these word problems.

Any help is greatly appreciated.

E.g

1.

A team of 15 employees, working 6 hours a day, does a job in 9 days. How many employees, working 9 hours a day, would be needed to do the same job in 5 days?

2.

A mixture of 100kg of tea at $20 per kg is made up of 60kg at $22 per kg and 40kg at a certain price. What is the price per kg of the second tea?

3.

In what proportion should one mix flour at $1.2 per kg with flour at $1.6 per kg to obtain a mixture at $1.35 per kg?